Web Services form a new distributed computing paradigm. Collaborative verification and validation are important when Web Services from different vendors are integrated together to carry out a coherent task. This paper presents a new approach to verify Web Services by model checking the process model of OWL-S (Web Ontology Language for Web Services) and to validate them by the test cases automatically generated in the model checking process. We extend the BLAST, a model checker that handles control flow model naturally, to handle the concurrency in OWL-S. We also propose enhancement in OWL-S and PDDL (Planning Domain Definition Language) to facilitate the automated test case generation. Experiments on realistic examples are provided to illustrate the process.