diff --git a/activesupport/lib/active_support/core_ext/object/blank.rb b/activesupport/lib/active_support/core_ext/object/blank.rb
index 8221dc4abe4509d47215e09f1a617cfe26d4e482..677ec1141ddfc29f21a264e3da6602bb2e79ce89 100644
--- a/activesupport/lib/active_support/core_ext/object/blank.rb
+++ b/activesupport/lib/active_support/core_ext/object/blank.rb
@@ -86,14 +86,18 @@ class Hash
 end
 
 class String
+  # 0x3000: fullwidth whitespace
+  NON_WHITESPACE_REGEXP = %r![^\s#{[0x3000].pack("U")}]!
+
   # A string is blank if it's empty or contains whitespaces only:
   #
   #   "".blank?                 # => true
   #   "   ".blank?              # => true
+  #   "　".blank?               # => true
   #   " something here ".blank? # => false
   #
   def blank?
-    self !~ /\S/
+    self !~ NON_WHITESPACE_REGEXP
   end
 end
 
diff --git a/activesupport/test/core_ext/blank_test.rb b/activesupport/test/core_ext/blank_test.rb
index 97c6b213ba2046e5c168a2d6fc400f3a67f73bcc..98ce8541a311cfd8c4fa64b152b66bcb5c76d6e8 100644
--- a/activesupport/test/core_ext/blank_test.rb
+++ b/activesupport/test/core_ext/blank_test.rb
@@ -2,7 +2,7 @@
 require 'active_support/core_ext/object/blank'
 
 class BlankTest < Test::Unit::TestCase
-  BLANK = [ EmptyTrue.new, nil, false, '', '   ', "  \n\t  \r ", [], {} ]
+  BLANK = [ EmptyTrue.new, nil, false, '', '   ', "  \n\t  \r ", '　', [], {} ]
   NOT   = [ EmptyFalse.new, Object.new, true, 0, 1, 'a', [nil], { nil => 0 } ]
 
   def test_blank