Is it possible to put Number validation in required field validator in asp.net text box?
You should use the CompareValidator, for example:
This is the most natural choice if you want a simple data type check. Otherwise if you want to verify a range use the RangeValidator suggestions. If you need a certain pattern use the RegularExpressionValidator.
Note that you'll want to add a RequiredFieldValidator as well since some validators will allow blank entries.