As per the EJB3 spec, Vector is not supported collection type for OneToMany mapping: anonymous wrote : | Collection-valued persistent fields and properties must be defined in terms of one of the following collection-valued interfaces regardless of whether the entity class otherwise adheres to the JavaBeans method conventions noted above and whether field or property-based access is used: | java.util.Collection, java.util.Set, java.util.List[4], java.util.Map.[5] | For collection-valued persistent properties, type T must be one of these collection interface types in the method signatures above. Generic variants of these collection types may also be used (for example, Set). | View the original post : http://www.jboss.com/index.html?module=bb&op=viewtopic&p=4144929#... Reply to the post : http://www.jboss.com/index.html?module=bb&op=posting&mode=reply&a...