Hi Ram K,
Could you please tell us what kind of validation are you trying to do? Is it client side or server side?
If it is client side, you can use GetHtml method of the RadEditor. You can find information in the following help article http://www.telerik.com/help/aspnet/editor/gethtml.html
If it is server side you can review the following article http://www.telerik.com/help/aspnet/editor/gettingsettingcontent.html
the Telerik team