Hi, I have found the answer googling. It is enough putting Response.Cache.SetCacheability(HttpCacheability.NoCache) in the Page_Load of pop up window. On the other hand here is the code snippet, Page1.aspx function DoDo(){ window.showModalDialog("Show.aspx","aa"); } LinkButton protected void Page_Load(object sender, EventArgs e) { Session["AA"] = "have a good day!"; } Show.aspx protected void Page_Load(object sender, EventArgs e) { if (Session["AA"] != null) Response.Write(Session["AA"].ToString()); else Response.Write("NULL.........."); } I hope this help to other people. Regards, Jose