Regular expression for date mm/dd/yyyy

 ^(0?[1-9]|[12][0-9]|3[01])[\/\-](0?[1-9]|1[012])[\/\-]\d{4}$

<asp:RegularExpressionValidator ID="RegularExpressionValidator1" runat="server"                            ControlToValidate="txtDOB"  ErrorMessage="*"  ForeColor="#CC0000"
 ValidationExpression="^(0?[1-9]|[12][0-9]|3[01])[\/\-](0?[1-9]|1[012])[\/\-]\d{4}$"></asp:RegularExpressionValidator>