Is an Action class object of Struts 1.x is a thread safe or not ? Can we make an Action class object as a thread safe object or not ?

In struts1.x front controller is ActionServlet. Each action class is a singleton class, so Action class object is not a thread safe, we need to make it as thread safe by applying synchronization

No, struts1 maintain action classes objects as instance pool thats why it is not thread safe.  you also  can't make action classs as thread safe. So don't use instance properties in action classes , use formbean instead.