validating dropdown

You can validate default selected index value of the drop down by using require field validator. As the validation process is executed at client side it reduce extra post back of your page. To do this you have to just out the require filed validator on page and set the default values of it such as ErrorMessage, ControlToValidate. To validate the default value of drop down you have to set the "InitialValue" property of validator to default value of it. here is the sample code