<!DOCTYPE html>
<html>
<head>
<script runat="server">
Sub DaySelect(obj As Object, e As DayRenderEventArgs)
If e.Day.IsWeekend Then
e.Day.IsSelectable = False
End If
End Sub
</script>
</head>
<body>
<form runat="server">
The weekends are not selectable
<asp:Calendar id="cal1" runat="server" OnDayRender="DaySelect"/>
</form>
</body>
</html>