You can the following to check the
FullForm of your code (makes it easy to understand how Mathematica's internal structures works. Check Mathematica's reference if you want to know details about this.
(* Result: Times[5.263`,Percent] *)
There you see that it is a simple multiplication (Head:
Times) of two elements. Then you can either use Albert Retey's solution or do a simple
(* Result: 5.263 *)
This is especially usefull if you have a more complex output like
(* Result: Times[299792458,Meter,Power[Second,-1]] *)
Then you can do a quick
(* Result: 299792458 *)
to get the value of this expression without the units.