Hello Tarun Singla,
Try to use combination of these settings like MaxLength
with the MinValue
For example if you set MinValue="0" and MaxValue="9999". Then you will be able to enter only numbers with length from 1 to 4 digits.
All the best,
the Telerik team
If you want to get updates on new releases, tips and tricks and sneak peeks at our product labs directly from the developers working on the RadControls for ASP.NET AJAX, subscribe to their blog feed