diff --git a/pandas/io/parsers.py b/pandas/io/parsers.py
index 44c7be853b6a0..292602feb01dc 100644
--- a/pandas/io/parsers.py
+++ b/pandas/io/parsers.py
@@ -21,6 +21,8 @@
 import pandas.lib as lib
 import pandas._parser as _parser
 from pandas.tseries.period import Period
+import json
+
 
 class DateConversionError(Exception):
     pass
@@ -1929,7 +1931,7 @@ class CellStyleConverter(object):
     """
 
     @staticmethod
-    def to_xls(style_dict):
+    def to_xls(style_dict, num_format_str=None):
         """
         converts a style_dict to an xlwt style object
         Parameters
@@ -1971,9 +1973,13 @@ def style_to_xlwt(item, firstlevel=True, field_sep=',', line_sep=';'):
 
         if style_dict:
             xlwt_stylestr = style_to_xlwt(style_dict)
-            return xlwt.easyxf(xlwt_stylestr, field_sep=',', line_sep=';')
+            style = xlwt.easyxf(xlwt_stylestr, field_sep=',', line_sep=';')
         else:
-            return xlwt.XFStyle()
+            style = xlwt.XFStyle()
+        if num_format_str is not None:
+            style.num_format_str = num_format_str
+
+        return style
 
     @staticmethod
     def to_xlsx(style_dict):
@@ -2111,13 +2117,26 @@ def _writecells_xls(self, cells, sheet_name, startrow, startcol):
             wks = self.book.add_sheet(sheet_name)
             self.sheets[sheet_name] = wks
 
+        style_dict = {}
+
         for cell in cells:
             val = _conv_value(cell.val)
-            style = CellStyleConverter.to_xls(cell.style)
-            if isinstance(val, datetime.datetime):
-                style.num_format_str = "YYYY-MM-DD HH:MM:SS"
-            elif isinstance(val, datetime.date):
-                style.num_format_str = "YYYY-MM-DD"
+
+            num_format_str = None
+            if isinstance(cell.val, datetime.datetime):
+                num_format_str = "YYYY-MM-DD HH:MM:SS"
+            if isinstance(cell.val, datetime.date):
+                num_format_str = "YYYY-MM-DD"
+
+            stylekey = json.dumps(cell.style)
+            if num_format_str:
+                stylekey += num_format_str
+
+            if stylekey in style_dict:
+                style = style_dict[stylekey]
+            else:
+                style = CellStyleConverter.to_xls(cell.style, num_format_str)
+                style_dict[stylekey] = style
 
             if cell.mergestart is not None and cell.mergeend is not None:
                 wks.write_merge(startrow + cell.row,