diff --git a/ChangeLog b/ChangeLog
index ea694293e8..6cef1290c1 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+Mon May 31 14:47:09 2010  NARUSE, Yui  <naruse@ruby-lang.org>
+
+	* string.c (rb_str_inspect): inspect as ASCII when the codepoint
+	  of a character in Unicode string is ASCII printable one.
+
 Mon May 31 13:44:40 2010  NARUSE, Yui  <naruse@ruby-lang.org>
 
 	* encoding.c (rb_enc_unicode_p): check the encoding is Unicode
diff --git a/string.c b/string.c
index ae4289380f..48ebf89815 100644
--- a/string.c
+++ b/string.c
@@ -4166,7 +4166,10 @@ rb_str_inspect(VALUE str)
 	else {
 	    if (p - n > prev) str_buf_cat(result, prev, p - n - prev);
 	    if (unicode_p) {
-		if (c < 0x10000) {
+		if (c < 0x100 && ISPRINT(c)) {
+		    snprintf(buf, CHAR_ESC_LEN, "%c", c);
+		}
+		else if (c < 0x10000) {
 		    snprintf(buf, CHAR_ESC_LEN, "\\u%04X", c);
 		}
 		else {
diff --git a/test/ruby/test_m17n.rb b/test/ruby/test_m17n.rb
index 6df58453d9..07cda751d1 100644
--- a/test/ruby/test_m17n.rb
+++ b/test/ruby/test_m17n.rb
@@ -221,6 +221,12 @@ class TestM17N < Test::Unit::TestCase
       str = "\u3042\u{10FFFD}"
       assert_equal(Encoding::UTF_8 == e ? %{"#{str}"} : '"\u3042\u{10FFFD}"', str.inspect)
     end
+    Encoding.default_external = Encoding::UTF_8
+    [Encoding::UTF_16BE, Encoding::UTF_16LE, Encoding::UTF_32BE, Encoding::UTF_32LE,
+      Encoding::UTF8_SOFTBANK].each do |e|
+      str = "abc".encode(e)
+      assert_equal('"abc"', str.inspect)
+    end
   ensure
     Encoding.default_internal = orig_int
     Encoding.default_external = orig_ext