diff --git a/ChangeLog b/ChangeLog
index c5d07d8628..3179cd408e 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,7 @@
+Sat Jul  2 00:58:00 2011  Kenta Murata  <mrkn@mrkn.jp>
+
+	* NEWS: describe a change of multiplication of Bignum.
+
 Fri Jul  1 18:52:31 2011  KOSAKI Motohiro  <kosaki.motohiro@gmail.com>
 
 	* benchmark/bm_app_erb.rb: increase loop count. too short
diff --git a/NEWS b/NEWS
index 4549688a61..bc8d8d9c7c 100644
--- a/NEWS
+++ b/NEWS
@@ -40,6 +40,11 @@ with all sufficient information, see the ChangeLog file.
     * extended method:
       * Array#pack supports endian modifiers
 
+  * Bignum
+    * Multiplication algorithm for Bignums with a large number of digits over
+      150 BDIGITs is changed in order to reduce its calculation time.
+      Now such large Bignums are multiplied by using Toom-3 algorithm.
+
   * Encoding
     * new encodings:
       * CP950