Is there any online service available to validate Web Service WSDL file?
Try out this site, although it requires you to upload the WSDL to some publicly accessible web site. I confirmed that it works against Google's WSDL, located here.
You can try using one of there tools: http://www.ws-i.org/deliverables/workinggroup.aspx?wg=testingtools
These will check both WSDL validity and Basic Profile 1.1 compliance.
If you're using Eclipse, just have your WSDL in a .wsdl file, eclipse will validate it automatically.
From the Doc
The WSDL validator handles validation according to the 4 step process defined above. Steps 1 and 2 are both delegated to Apache Xerces (and XML parser). Step 3 is handled by the WSDL validator and any extension namespace validators (more on extensions below). Step 4 is handled by any declared custom validators (more on this below as well). Each step must pass in order for the next step to run.
I've found http://www.validwsdl.com/ to be useful, since it also allows calling into the methods, if available.