hi Friend,
in nested Gridview you have to you use FindControl Method for find the control of any Gridview For Example: Suppose we have GridvView1 Contain nested GridView2 and GridView2 Contain RadioButton Control then
Dim grd As GridView = CType(Gridview1.Rows(0).FindControl("GridViewname"), GridView)
For Each dr As DataGridItem In grd.Rows
Dim rd As RadioButton = CType(dr.FindControl("Radiobuttonname"), RadioButton)
''rd.Checked use this this method
Next
Hope this will help :)