diff --git a/README.md b/README.md
index f0baf39..367f7e4 100644
--- a/README.md
+++ b/README.md
@@ -107,7 +107,8 @@ make test
   * python 2.7,
   * virtualenv,
   * luacheck,
-  * >=tarantool/shard-1.1-92-gec1a27e (but < 2.0).
+  * >=tarantool/shard-1.1-92-gec1a27e (but < 2.0),
+  * >=tarantool/avro-schema-2.2.2-4-g1145e3e.
 * For building apidoc (additionally to 'for use'):
   * ldoc.
 
diff --git a/graphql/core/schema.lua b/graphql/core/schema.lua
index a03093e..a320335 100644
--- a/graphql/core/schema.lua
+++ b/graphql/core/schema.lua
@@ -50,6 +50,12 @@ function schema:generateTypeMap(node)
   node.fields = type(node.fields) == 'function' and node.fields() or node.fields
   self.typeMap[node.name] = node
 
+  if node.__type == 'Union' then
+    for _, type in ipairs(node.types) do
+      self:generateTypeMap(type)
+    end
+  end
+
   if node.__type == 'Object' and node.interfaces then
     for _, interface in ipairs(node.interfaces) do
       self:generateTypeMap(interface)
diff --git a/graphql/tarantool_graphql.lua b/graphql/tarantool_graphql.lua
index 394e871..70bccd2 100644
--- a/graphql/tarantool_graphql.lua
+++ b/graphql/tarantool_graphql.lua
@@ -86,6 +86,8 @@ local function avro_type(avro_schema)
             return 'string'
         elseif avro_schema == 'string*' then
             return 'string*'
+        elseif avro_schema == 'null' then
+            return 'null'
         end
     end
     error('unrecognized avro-schema type: ' .. json.encode(avro_schema))
@@ -252,8 +254,10 @@ local function convert_record_fields_to_args(fields, opts)
         if not skip_compound or (
                 avro_t ~= 'record' and avro_t ~= 'record*' and
                 avro_t ~= 'array' and avro_t ~= 'array*' and
-                avro_t ~= 'map' and avro_t ~= 'map*') then
-            local gql_class = gql_argument_type(field.type)
+                avro_t ~= 'map' and avro_t ~= 'map*' and
+                avro_t ~= 'union') then
+
+            local gql_class = gql_argument_type(field.type, field.name)
             args[field.name] = nullable(gql_class)
         end
     end
@@ -277,7 +281,7 @@ local function convert_record_fields(state, fields)
 
         res[field.name] = {
             name = field.name,
-            kind = gql_type(state, field.type),
+            kind = gql_type(state, field.type, nil, nil, field.name),
         }
     end
     return res
@@ -670,6 +674,213 @@ local convert_connection_to_field = function(state, connection, collection_name)
     end
 end
 
+--- The function 'boxes' given GraphQL type into GraphQL Object 'box' type.
+---
+--- @tparam table gql_type GraphQL type to be boxed
+--- @tparam string avro_name type (or name, in record case) of avro-schema which
+--- was used to create `gql_type`. `avro_name` is used to provide avro-valid names
+--- for fields of boxed types
+--- @treturn table GraphQL Object
+local function box_type(gql_type, avro_name)
+    check(gql_type, 'gql_type', 'table')
+
+    local gql_true_type = nullable(gql_type)
+
+    local box_name = gql_true_type.name or gql_true_type.__type
+    box_name = box_name .. '_box'
+
+    local box_fields = {[avro_name] = {name = avro_name, kind = gql_type}}
+
+    return types.object({
+        name = box_name,
+        description = 'Box (wrapper) around union variant',
+        fields = box_fields,
+    })
+end
+
+--- The functions creates table of GraphQL types from avro-schema union type.
+local function create_union_types(avro_schema, state)
+    check(avro_schema, 'avro_schema', 'table')
+    assert(utils.is_array(avro_schema), 'union avro-schema must be an array ' ..
+        ', got\n' .. yaml.encode(avro_schema))
+
+    local union_types = {}
+    local determinant_to_type = {}
+    local is_nullable = false
+
+    for _, type in ipairs(avro_schema) do
+        -- If there is a 'null' type among 'union' types (in avro-schema union)
+        -- then resulting GraphQL Union type will be nullable
+        if type == 'null' then
+            is_nullable = true
+        else
+            local variant_type = gql_type(state, type)
+            local box_field_name = type.name or avro_type(type)
+            union_types[#union_types + 1] = box_type(variant_type, box_field_name)
+            local determinant = type.name or type.type or type
+            determinant_to_type[determinant] = union_types[#union_types]
+        end
+    end
+
+    return union_types, determinant_to_type, is_nullable
+end
+
+--- The function creates GraphQL Union type from given avro-schema union type.
+--- There are two problems with GraphQL Union types, which we solve with specific
+--- format of generated Unions. These problems are:
+--- 1) GraphQL Unions represent an object that could be one of a list of
+--- GraphQL Object types. So Scalars and Lists can not be one of Union types.
+--- 2) GraphQL responses, received from tarantool graphql, must be avro-valid.
+--- On every incoming GraphQL query a corresponding avro-schema can be generated.
+--- Response to this query is 'avro-valid' if it can be successfully validated with
+--- this generated (from incoming query) avro-schema.
+---
+--- Specific format of generated Unions include the following:
+---
+--- Avro scalar types (e.g. int, string) are converted into GraphQL Object types.
+--- Avro scalar converted to GraphQL Scalar (string -> String) and then name of
+--- GraphQL type is concatenated with '_box' ('String_box'). Resulting name is a name
+--- of created GraphQL Object. This object has only one field with GraphQL type
+--- corresponding to avro scalar type (String type in our example). Avro type's
+--- name is taken as a name for this single field.
+---     [..., "string", ...]
+--- turned into
+---     MyUnion {
+---         ...
+---         ... on String_box {
+---             string
+---         ...
+---     }
+---
+--- Avro arrays and maps are converted into GraphQL Object types. The name of
+--- the resulting GraphQL Object is 'List_box' or 'Map_box' respectively. This
+--- object has only one field with GraphQL type corresponding to 'items'/'values'
+--- avro type. 'array' or 'map' (respectively) is taken as a name of this
+--- single field.
+---     [..., {"type": "array", "items": "int"}, ...]
+--- turned into
+---     MyUnion {
+---         ...
+---         ... on List_box {
+---             array
+---         ...
+---     }
+---
+--- Avro records are converted into GraphQL Object types. The name of the resulting
+--- GraphQL Object is concatenation of record's name and '_box'. This Object
+--- has only one field. The name of this field is record's name. The type of this
+--- field is GraphQL Object generated from avro record schema in a usual way
+--- (see @{gql_type})
+---
+---     { "type": "record", "name": "Foo", "fields":[
+---         { "name": "foo1", "type": "string" },
+---         { "name": "foo2", "type": "string" }
+---     ]}
+--- turned into
+---     MyUnion {
+---         ...
+---         ... on Foo_box {
+---             Foo {
+---                 foo1
+---                 foo2
+---             }
+---         ...
+---     }
+---
+--- Please consider full example below.
+---
+--- @tparam table state
+--- @tparam table avro_schema avro-schema union type
+--- @tparam string union_name name for resulting GraphQL Union type
+--- @treturn table GraphQL Union type. Consider the following example:
+--- Avro-schema (inside a record):
+---     ...
+---     "name": "MyUnion", "type": [
+---         "null",
+---         "string",
+---         { "type": "array", "items": "int" },
+---         { "type": "record", "name": "Foo", "fields":[
+---             { "name": "foo1", "type": "string" },
+---             { "name": "foo2", "type": "string" }
+---         ]}
+---     ]
+---     ...
+--- GraphQL Union type (It will be nullable as avro-schema has 'null' variant):
+---     MyUnion {
+---         ... on String_box {
+---             string
+---         }
+---
+---         ... on List_box {
+---             array
+---         }
+---
+---         ... on Foo_box {
+---             Foo {
+---                 foo1
+---                 foo2
+---             }
+---     }
+local function create_gql_union(state, avro_schema, union_name)
+    check(avro_schema, 'avro_schema', 'table')
+    assert(utils.is_array(avro_schema), 'union avro-schema must be an array, ' ..
+    ' got ' .. yaml.encode(avro_schema))
+
+    -- check avro-schema constraints
+    for i, type in ipairs(avro_schema) do
+        assert(avro_type(type) ~= 'union', 'unions must not immediately ' ..
+        'contain other unions')
+
+        if type.name ~= nil then
+            for j, another_type in ipairs(avro_schema) do
+                if i ~= j then
+                    if another_type.name ~= nil then
+                        assert(type.name:gsub('%*$', '') ~=
+                            another_type.name:gsub('%*$', ''),
+                            'Unions may not contain more than one schema with ' ..
+                                'the same name')
+                    end
+                end
+            end
+        else
+            for j, another_type in ipairs(avro_schema) do
+                if i ~= j then
+                    assert(avro_type(type) ~= avro_type(another_type),
+                        'Unions may not contain more than one schema with ' ..
+                            'the same type except for the named types: ' ..
+                            'record, fixed and enum')
+                end
+            end
+        end
+    end
+
+    -- create GraphQL union
+    local union_types, determinant_to_type, is_nullable =
+        create_union_types(avro_schema, state)
+
+    local union_type = types.union({
+        types = union_types,
+        name = union_name,
+        resolveType = function(result)
+            for determinant, type in pairs(determinant_to_type) do
+                if result[determinant] ~= nil then
+                    return type
+                end
+            end
+            error(('result object has no determinant field matching ' ..
+                'determinants for this union\nresult object:\n%sdeterminants:\n%s')
+                    :format(yaml.encode(result),
+                        yaml.encode(determinant_to_type)))
+        end
+    })
+
+    if not is_nullable then
+        union_type = types.nonNull(union_type)
+    end
+
+    return union_type
+end
+
 --- The function converts passed avro-schema to a GraphQL type.
 ---
 --- @tparam table state for read state.accessor and previously filled
@@ -677,7 +888,10 @@ end
 --- @tparam table avro_schema input avro-schema
 --- @tparam[opt] table collection table with schema_name, connections fields
 --- described a collection (e.g. tarantool's spaces)
----
+--- @tparam[opt] string collection_name name of `collection`
+--- @tparam[opt] string field_name it is only for an union generation,
+--- because avro-schema union has no name in it and specific name is necessary
+--- for GraphQL union
 --- If collection is passed, two things are changed within this function:
 ---
 --- 1. Connections from the collection will be taken into account to
@@ -688,7 +902,7 @@ end
 --- XXX As it is not clear now what to do with complex types inside arrays
 --- (just pass to results or allow to use filters), only scalar arrays
 --- is allowed for now. Note: map is considered scalar.
-gql_type = function(state, avro_schema, collection, collection_name)
+gql_type = function(state, avro_schema, collection, collection_name, field_name)
     assert(type(state) == 'table',
         'state must be a table, got ' .. type(state))
     assert(avro_schema ~= nil,
@@ -763,6 +977,8 @@ gql_type = function(state, avro_schema, collection, collection_name)
 
         local gql_map = types_map
         return avro_t == 'map' and types.nonNull(gql_map) or gql_map
+    elseif avro_t == 'union' then
+        return create_gql_union(state, avro_schema, field_name)
     else
         local res = convert_scalar_type(avro_schema, {raise = false})
         if res == nil then
diff --git a/graphql/utils.lua b/graphql/utils.lua
index 89def8c..2dee7da 100644
--- a/graphql/utils.lua
+++ b/graphql/utils.lua
@@ -204,4 +204,13 @@ function utils.table_size(t)
     return count
 end
 
+function utils.value_in(value, array)
+    for _, v in ipairs(array) do
+        if value == v then
+            return true
+        end
+    end
+    return false
+end
+
 return utils
diff --git a/test/local/avro_union.result b/test/local/avro_union.result
new file mode 100644
index 0000000..ab9fda8
--- /dev/null
+++ b/test/local/avro_union.result
@@ -0,0 +1,82 @@
+RESULT
+---
+user_collection:
+- user_id: user_id_0
+  name: Nobody
+- user_id: user_id_1
+  name: Zlata
+  stuff:
+    string: Some string
+- user_id: user_id_2
+  name: Ivan
+  stuff:
+    int: 123
+- user_id: user_id_3
+  name: Jane
+  stuff:
+    map: {'salary': 333, 'deposit': 444}
+- user_id: user_id_4
+  name: Dan
+  stuff:
+    Foo:
+      foo1: foo1 string
+      foo2: foo2 string
+- user_id: user_id_5
+  name: Max
+  stuff:
+    array:
+    - {'salary': 'salary string', 'deposit': 'deposit string'}
+    - {'salary': 'string salary', 'deposit': 'string deposit'}
+...
+
+Validating results with initial avro-schema
+true
+---
+user_id: user_id_0
+name: Nobody
+...
+
+true
+---
+user_id: user_id_1
+name: Zlata
+stuff:
+  string: Some string
+...
+
+true
+---
+user_id: user_id_2
+name: Ivan
+stuff:
+  int: 123
+...
+
+true
+---
+user_id: user_id_3
+name: Jane
+stuff:
+  map: {'salary': 333, 'deposit': 444}
+...
+
+true
+---
+user_id: user_id_4
+name: Dan
+stuff:
+  Foo:
+    foo1: foo1 string
+    foo2: foo2 string
+...
+
+true
+---
+user_id: user_id_5
+name: Max
+stuff:
+  array:
+  - {'salary': 'salary string', 'deposit': 'deposit string'}
+  - {'salary': 'string salary', 'deposit': 'string deposit'}
+...
+
diff --git a/test/local/avro_union.test.lua b/test/local/avro_union.test.lua
new file mode 100755
index 0000000..bce9179
--- /dev/null
+++ b/test/local/avro_union.test.lua
@@ -0,0 +1,161 @@
+#!/usr/bin/env tarantool
+
+local fio = require('fio')
+
+-- require in-repo version of graphql/ sources despite current working directory
+package.path = fio.abspath(debug.getinfo(1).source:match("@?(.*/)"):
+    gsub('/./', '/'):gsub('/+$', '')) .. '/../../?.lua' .. ';' .. package.path
+
+box.cfg{ background = false }
+local json = require('json')
+local yaml = require('yaml')
+local graphql = require('graphql')
+local utils = require('graphql.utils')
+local avro_schema = require('avro_schema')
+
+local schemas = json.decode([[{
+    "user_collection": {
+        "name": "user_collection",
+        "type": "record",
+        "fields": [
+            { "name": "user_id", "type": "string" },
+            { "name": "name", "type": "string" },
+            { "name": "stuff", "type": [
+                "null",
+                "string",
+                "int",
+                { "type": "map", "values": "int" },
+                { "type": "record", "name": "Foo", "fields":[
+                    { "name": "foo1", "type": "string" },
+                    { "name": "foo2", "type": "string" }
+                ]},
+                {"type":"array","items": { "type":"map","values":"string" } }
+            ]}
+        ]
+    }
+}]])
+
+local collections = json.decode([[{
+    "user_collection": {
+        "schema_name": "user_collection",
+        "connections": []
+    }
+}]])
+
+local service_fields = {
+    user_collection = {
+        {name = 'expires_on', type = 'long', default = 0}
+    }
+}
+
+local indexes = {
+    user_collection = {
+        user_id_index = {
+            service_fields = {},
+            fields = {'user_id'},
+            index_type = 'tree',
+            unique = true,
+            primary = true,
+        }
+    }
+}
+
+local USER_ID_FIELD = 2
+
+box.schema.create_space('user_collection')
+box.space.user_collection:create_index('user_id_index',
+    {type = 'tree', unique = true, parts = { USER_ID_FIELD, 'string' }}
+)
+
+local NULL = 0
+local STRING = 1
+local INT = 2
+local MAP = 3
+local OBJ = 4
+local ARR_MAP = 5
+
+box.space.user_collection:replace(
+    {1827767717, 'user_id_0', 'Nobody', NULL, box.NULL})
+
+box.space.user_collection:replace(
+    {1827767717, 'user_id_1', 'Zlata', STRING, 'Some string'})
+
+box.space.user_collection:replace(
+    {1827767717, 'user_id_2', 'Ivan', INT, 123})
+
+box.space.user_collection:replace(
+    {1827767717, 'user_id_3', 'Jane', MAP, {salary = 333, deposit = 444}})
+
+box.space.user_collection:replace(
+    {1827767717, 'user_id_4', 'Dan', OBJ, {'foo1 string', 'foo2 string'}})
+
+box.space.user_collection:replace(
+    {1827767717, 'user_id_5', 'Max', ARR_MAP,
+     {{salary = 'salary string', deposit = 'deposit string'},
+     {salary = 'string salary', deposit = 'string deposit'}}})
+
+local accessor = graphql.accessor_space.new({
+    schemas = schemas,
+    collections = collections,
+    service_fields = service_fields,
+    indexes = indexes,
+})
+
+local gql_wrapper = graphql.new({
+    schemas = schemas,
+    collections = collections,
+    accessor = accessor,
+})
+
+local query_1 = [[
+    query user_collection {
+        user_collection {
+            user_id
+            name
+            stuff {
+                ... on String_box {
+                    string
+                }
+
+                ... on Int_box {
+                    int
+                }
+
+                ... on List_box {
+                    array
+                }
+
+                ... on Map_box {
+                    map
+                }
+
+                ... on Foo_box {
+                    Foo {
+                        foo1
+                        foo2
+                    }
+                }
+            }
+        }
+    }
+]]
+
+utils.show_trace(function()
+    local variables_1 = {}
+    local gql_query_1 = gql_wrapper:compile(query_1)
+    local result = gql_query_1:execute(variables_1)
+    print(('RESULT\n%s'):format(yaml.encode(result)))
+
+    print('Validating results with initial avro-schema')
+    local _, schema = avro_schema.create(schemas.user_collection)
+    for _, r in ipairs(result.user_collection) do
+        local ok, err = avro_schema.validate(schema, r)
+        print(ok)
+        if not ok then print(err) end
+        print(yaml.encode(r))
+    end
+end)
+
+box.space.user_collection:drop()
+
+os.exit()