diff --git a/hadoop-mapreduce-project/CHANGES.txt b/hadoop-mapreduce-project/CHANGES.txt
index 657b4414dcf..38982e40a11 100644
--- a/hadoop-mapreduce-project/CHANGES.txt
+++ b/hadoop-mapreduce-project/CHANGES.txt
@@ -288,6 +288,9 @@ Release 2.7.0 - UNRELEASED
     MAPREDUCE-4431. mapred command should print the reason on killing already 
     completed jobs. (devaraj via ozawa)
 
+    MAPREDUCE-6255. Fix JobCounter's format to use grouping separator.
+    (Ryu Kobayashi via ozawa)
+
   OPTIMIZATIONS
 
     MAPREDUCE-6169. MergeQueue should release reference to the current item 
diff --git a/hadoop-mapreduce-project/hadoop-mapreduce-client/hadoop-mapreduce-client-app/src/main/java/org/apache/hadoop/mapreduce/v2/app/webapp/CountersBlock.java b/hadoop-mapreduce-project/hadoop-mapreduce-client/hadoop-mapreduce-client-app/src/main/java/org/apache/hadoop/mapreduce/v2/app/webapp/CountersBlock.java
index 1b20c5dc4ed..568658e1587 100644
--- a/hadoop-mapreduce-project/hadoop-mapreduce-client/hadoop-mapreduce-client-app/src/main/java/org/apache/hadoop/mapreduce/v2/app/webapp/CountersBlock.java
+++ b/hadoop-mapreduce-project/hadoop-mapreduce-client/hadoop-mapreduce-client-app/src/main/java/org/apache/hadoop/mapreduce/v2/app/webapp/CountersBlock.java
@@ -139,10 +139,10 @@ public class CountersBlock extends HtmlBlock {
           Counter mc = mg == null ? null : mg.findCounter(counter.getName());
           Counter rc = rg == null ? null : rg.findCounter(counter.getName());
           groupRow.
-            td(mc == null ? "0" : String.valueOf(mc.getValue())).
-            td(rc == null ? "0" : String.valueOf(rc.getValue()));
+            td(mc == null ? "0" : String.format("%,d", mc.getValue())).
+            td(rc == null ? "0" : String.format("%,d", rc.getValue()));
         }
-        groupRow.td(String.valueOf(counter.getValue()))._();
+        groupRow.td(String.format("%,d", counter.getValue()))._();
       }
       group._()._()._()._();
     }