diff --git a/asv_bench/benchmarks/frame_methods.py b/asv_bench/benchmarks/frame_methods.py
index 2c07c28066faf..9367c42f8d39a 100644
--- a/asv_bench/benchmarks/frame_methods.py
+++ b/asv_bench/benchmarks/frame_methods.py
@@ -582,7 +582,7 @@ def time_frame_interpolate_some_good_infer(self):
         self.df.interpolate(downcast='infer')
 
 
-class frame_isnull(object):
+class frame_isnull_floats_no_null(object):
     goal_time = 0.2
 
     def setup(self):
@@ -593,6 +593,33 @@ def time_frame_isnull(self):
         isnull(self.df)
 
 
+class frame_isnull_floats(object):
+    goal_time = 0.2
+
+    def setup(self):
+        np.random.seed(1234)
+        self.sample = np.array([np.nan, 1.0])
+        self.data = np.random.choice(self.sample, (1000, 1000))
+        self.df = DataFrame(self.data)
+
+    def time_frame_isnull(self):
+        isnull(self.df)
+
+
+class frame_isnull_obj(object):
+    goal_time = 0.2
+
+    def setup(self):
+        np.random.seed(1234)
+        self.sample = np.array([NaT, np.nan, None, np.datetime64('NaT'),
+                                np.timedelta64('NaT'), 0, 1, 2.0, '', 'abcd'])
+        self.data = np.random.choice(self.sample, (1000, 1000))
+        self.df = DataFrame(self.data)
+
+    def time_frame_isnull(self):
+        isnull(self.df)
+
+
 class frame_iteritems(object):
     goal_time = 0.2
 
diff --git a/doc/source/whatsnew/v0.17.1.txt b/doc/source/whatsnew/v0.17.1.txt
index f2008727017f8..f8801cfdf9785 100755
--- a/doc/source/whatsnew/v0.17.1.txt
+++ b/doc/source/whatsnew/v0.17.1.txt
@@ -156,6 +156,7 @@ Bug Fixes
 - Bug in output formatting when using an index of ambiguous times (:issue:`11619`)
 - Bug in comparisons of Series vs list-likes (:issue:`11339`)
 - Bug in ``DataFrame.replace`` with a ``datetime64[ns, tz]`` and a non-compat to_replace (:issue:`11326`, :issue:`11153`)
+- Bug in ``isnull`` where ``numpy.datetime64('NaT')`` in a ``numpy.array`` was not determined to be null(:issue:`11206`)
 - Bug in list-like indexing with a mixed-integer Index (:issue:`11320`)
 - Bug in ``pivot_table`` with ``margins=True`` when indexes are of ``Categorical`` dtype (:issue:`10993`)
 - Bug in ``DataFrame.plot`` cannot use hex strings colors (:issue:`10299`)
diff --git a/pandas/lib.pyx b/pandas/lib.pyx
index 1a1f04cba1cb9..f7978c4791538 100644
--- a/pandas/lib.pyx
+++ b/pandas/lib.pyx
@@ -1,3 +1,4 @@
+# cython: profile=False
 cimport numpy as np
 cimport cython
 import numpy as np
@@ -54,7 +55,8 @@ from datetime import datetime as pydatetime
 # this is our tseries.pxd
 from datetime cimport *
 
-from tslib cimport convert_to_tsobject, convert_to_timedelta64
+from tslib cimport (convert_to_tsobject, convert_to_timedelta64,
+                    _check_all_nulls)
 import tslib
 from tslib import NaT, Timestamp, Timedelta
 
@@ -245,8 +247,6 @@ def time64_to_datetime(ndarray[int64_t, ndim=1] arr):
 
     return result
 
-cdef inline int64_t get_timedelta64_value(val):
-    return val.view('i8')
 
 #----------------------------------------------------------------------
 # isnull / notnull related
@@ -346,10 +346,10 @@ def isnullobj(ndarray[object] arr):
     cdef ndarray[uint8_t] result
 
     n = len(arr)
-    result = np.zeros(n, dtype=np.uint8)
+    result = np.empty(n, dtype=np.uint8)
     for i from 0 <= i < n:
         val = arr[i]
-        result[i] = val is NaT or _checknull(val)
+        result[i] = _check_all_nulls(val)
     return result.view(np.bool_)
 
 @cython.wraparound(False)
diff --git a/pandas/src/datetime.pxd b/pandas/src/datetime.pxd
index f2f764c785894..5f7de8244d17e 100644
--- a/pandas/src/datetime.pxd
+++ b/pandas/src/datetime.pxd
@@ -1,3 +1,4 @@
+# cython: profile=False
 from numpy cimport int64_t, int32_t, npy_int64, npy_int32, ndarray
 from cpython cimport PyObject
 
@@ -59,6 +60,7 @@ cdef extern from "numpy/ndarrayobject.h":
 
 cdef extern from "numpy_helper.h":
     npy_datetime get_datetime64_value(object o)
+    npy_timedelta get_timedelta64_value(object o)
 
 cdef extern from "numpy/npy_common.h":
 
diff --git a/pandas/src/numpy_helper.h b/pandas/src/numpy_helper.h
index 8b79bbe79ff2f..9f406890c4e68 100644
--- a/pandas/src/numpy_helper.h
+++ b/pandas/src/numpy_helper.h
@@ -40,7 +40,11 @@ get_nat(void) {
 PANDAS_INLINE npy_datetime
 get_datetime64_value(PyObject* obj) {
   return ((PyDatetimeScalarObject*) obj)->obval;
+}
 
+PANDAS_INLINE npy_timedelta
+get_timedelta64_value(PyObject* obj) {
+  return ((PyTimedeltaScalarObject*) obj)->obval;
 }
 
 PANDAS_INLINE int
diff --git a/pandas/tests/test_common.py b/pandas/tests/test_common.py
index 89826209fa46d..57448e2d018dc 100644
--- a/pandas/tests/test_common.py
+++ b/pandas/tests/test_common.py
@@ -179,6 +179,13 @@ def test_isnull_nat():
     exp = np.array([True])
     assert(np.array_equal(result, exp))
 
+def test_isnull_numpy_nat():
+    arr = np.array([NaT, np.datetime64('NaT'), np.timedelta64('NaT'),
+                    np.datetime64('NaT', 's')])
+    result = isnull(arr)
+    expected = np.array([True] * 4)
+    tm.assert_numpy_array_equal(result, expected)
+
 def test_isnull_datetime():
     assert (not isnull(datetime.now()))
     assert notnull(datetime.now())
diff --git a/pandas/tslib.pxd b/pandas/tslib.pxd
index 3cb7e94c65100..5e0c88604206c 100644
--- a/pandas/tslib.pxd
+++ b/pandas/tslib.pxd
@@ -7,3 +7,4 @@ cdef bint _is_utc(object)
 cdef bint _is_tzlocal(object)
 cdef object _get_dst_info(object)
 cdef bint _nat_scalar_rules[6]
+cdef bint _check_all_nulls(obj)
diff --git a/pandas/tslib.pyx b/pandas/tslib.pyx
index 0d47c2526df14..713cf08bfc3e2 100644
--- a/pandas/tslib.pyx
+++ b/pandas/tslib.pyx
@@ -3,6 +3,7 @@
 cimport numpy as np
 from numpy cimport (int8_t, int32_t, int64_t, import_array, ndarray,
                     NPY_INT64, NPY_DATETIME, NPY_TIMEDELTA)
+from datetime cimport get_datetime64_value, get_timedelta64_value
 import numpy as np
 
 # GH3363
@@ -707,12 +708,28 @@ NaT = NaTType()
 
 iNaT = util.get_nat()
 
-
 cdef inline bint _checknull_with_nat(object val):
     """ utility to check if a value is a nat or not """
     return val is None or (
         PyFloat_Check(val) and val != val) or val is NaT
 
+cdef inline bint _check_all_nulls(object val):
+    """ utility to check if a value is any type of null """
+    cdef bint res
+    if PyFloat_Check(val):
+        res = val != val
+    elif val is NaT:
+        res = 1
+    elif val is None:
+        res = 1
+    elif is_datetime64_object(val):
+        res = get_datetime64_value(val) == NPY_NAT
+    elif is_timedelta64_object(val):
+        res = get_timedelta64_value(val) == NPY_NAT
+    else:
+        res = 0
+    return res
+
 cdef inline bint _cmp_nat_dt(_NaT lhs, _Timestamp rhs, int op) except -1:
     return _nat_scalar_rules[op]