Hello Sapan

   Microsoft® ASP.NET view state, in a nutshell, is the technique used by an ASP.NET Web page to persist changes to the state of a Web Form across postbacks.The view state of a page is, by default, placed in a hidden form field named __VIEWSTATE. 

 For more details please refer to :

 http://msdn.microsoft.com/en-us/library/ms972976.aspx