Are you using the service.bat file provided with AS 5.1.0.GA to run it as a service? Or are you using some other tool? If so, provide the full URL for that tool. If you are using service.bat, I think I might know what the problem is - the JVM options were moved to run-conf.bat, and run.bat is probably not finding it when you run as a service. Grab Process Monitor from sysinternals and run it. That will tell you the full java command line used to run the app server, see if it contains the heap settings. View the original post : http://www.jboss.org/index.html?module=bb&op=viewtopic&p=4239861#... Reply to the post : http://www.jboss.org/index.html?module=bb&op=posting&mode=reply&a...