I do have a simple EJB3 application in JBoss-4.2.3 GA in which i have the singleton MDB working. So please post your code in the MDB (along with the annotations) and also the steps that you are following to test that only one instance is created. While posting the logs or code or xml content, remember to wrap it in a code block using the Code button in the message editor window and please hit the Preview button to make sure your post is correctly formatted View the original post : http://www.jboss.com/index.html?module=bb&op=viewtopic&p=4190065#... Reply to the post : http://www.jboss.com/index.html?module=bb&op=posting&mode=reply&a...