diff --git a/ChangeLog b/ChangeLog
index 8d35baf50d..b6ebb22a19 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+Mon Jul 21 13:55:37 2008  Nobuyoshi Nakada  <nobu@ruby-lang.org>
+
+	* README.EXT, README.EXT.ja (1.5 Manipulating Ruby data): mentioned
+	  rb_sprintf and rb_vsprintf.  [ruby-dev:35611]
+
 Mon Jul 21 10:25:52 2008  Nobuyoshi Nakada  <nobu@ruby-lang.org>
 
 	* io.c (prepare_getline_args): check if rs is a string when non-nil
diff --git a/README.EXT b/README.EXT
index 509bffba32..b41e6a426c 100644
--- a/README.EXT
+++ b/README.EXT
@@ -189,6 +189,11 @@ listed below:
 
     Appends len bytes of data from ptr to the Ruby string.
 
+  rb_sprintf(const char *format, ...)
+  rb_vsprintf(const char *format, ...)
+
+    Creates a new Ruby string with printf(3) format.
+
  Array functions
 
   rb_ary_new()
diff --git a/README.EXT.ja b/README.EXT.ja
index 23bf774744..0205254ad6 100644
--- a/README.EXT.ja
+++ b/README.EXT.ja
@@ -216,6 +216,11 @@ Ruby
 
     Rubyの文字列strにlenバイトの文字列ptrを追加する．
 
+  rb_sprintf(const char *format, ...)
+  rb_vsprintf(const char *format, ...)
+
+    printf(3)のフォーマットにしたがって，Rubyの文字列を生成する．
+
  配列に対する関数
 
   rb_ary_new()