<asp:RadioButtonList ID="rb" runat="server">
<asp:ListItem Text="Administrator" Value="1"></asp:ListItem>
<asp:ListItem Text="User" Value="2"></asp:ListItem>
</asp:RadioButtonList>
string ug = "1";
if (ug == "1")
rb.SelectedValue = ug;
else
rb.SelectedValue = ug;