both operator is used for object conversion. Is operator is a boolean type operator. so it return true if succeed case and return false in the fail case.on the other hand As operator return null if conversion fail.

//The is operator is used to check whether the run-time type of an object is compatible with a given object num=10; if (num is int) { Response.Write("Num is integer"); } //The as operator is used to perform conversions between compatible types. object ss = "This sis the string"; string str = string.Empty; if (ss is string) { str = ss as string; Response.Write(str); }

There are a few keywords one should be aware of:

The as operator is similar to a cast but on any conversion failure null is returned as oppose to raising an exception. Note: it will not do the conversion (cast != data type conversion)! 

Personally, I prefer not to use this operator, and, instead, use:

      if (x is MyType)

// do the logic

      else

// log error

As you can see, the is operator, which existed for some time, is used to check whether the run-time type of an object is compatible with a given type.

However, there are cases where as operator is useful.  For example, I've personally used it in helper classes as described by code snippet below:

    public class CompareHelper

    {

        public int Compare(object data1, object data2)   // similar to string.compare

        {

            int result = 0;  

            if (typeof(T) == typeof(bool))

                result = Compare(data1 as bool, data2 as bool);

            else if (typeof(T) == typeof(string))

                result = Compare(data1 as string, data2 as string);

           else if (typeof(T) == typeof(SomeCustomClass))   // perhaps this calls for some property call

                result = Compare(data1 == null ? 0m : (data1 as SomeCustomClass).SomeDecimalProperty, data2 == null ? 0m : (data2 as SomeCustomClass).SomeDecimalProperty);

            . . .

        }

        public int Compare(bool data1, bool data 2)

        {

             . . .

        }

        public int Compare(decimal data1, decimal data 2)

        {

             . . .

        }

        . . .

    }