More observations on this bug. I have isolated the problem. If I used WebsphereTransactionManagerLookup for WAS6.0 instead of WebsphereExtendedJTATransactionLookup ( as was indicated in the manuals) in hibernate.cfg.xml, <property name="hibernate.transaction.manager_lookup_class">org.hibernate.transaction.WebSphereTransactionManagerLookup</property> I do not see the UnsupportedOperationException being thrown. But I do not know yet the implications of using WebsphereTransactionmanagerLookup which is meant for WAS 5.1 on WAS 6.0. Can someone clarify? View the original post : http://www.jboss.com/index.html?module=bb&op=viewtopic&p=3994885#... Reply to the post : http://www.jboss.com/index.html?module=bb&op=posting&mode=reply&a...