<asp:ScriptManager ID="ScriptManager1" runat="server">
</asp:ScriptManager>

<asp:TextBox ID="tbYmd" runat="server" MaxLength="10" Width="80px"></asp:TextBox>

<AjaxToolkit:MaskedEditExtender ID="MaskedEditExtender1" runat="server"
 TargetControlID="tbYmd"
        Mask="9999/99/99"
        MaskType="Date"
        UserDateFormat="YearMonthDay">
</AjaxToolkit:MaskedEditExtender>

<asp:ScriptManager ID="ScriptManager1" runat="server">
</asp:ScriptManager>

<asp:TextBox ID="tbYmd" runat="server" MaxLength="10" Width="80px"></asp:TextBox>

<AjaxToolkit:CalendarExtender
    ID="CalendarExtender1"
    runat="server"
    TargetControlID="tbYmd"
    Format="yyyy/MM/dd">
</AjaxToolkit:CalendarExtender>