Web Ontology Language for Services (OWL-S) is a standard XML-based language for specifying workflows and integration semantics among Web services (WS), which form composite WS. This paper analyzes the fault patterns of OWL-S specified composite WS and their workflows, proposes an ontology-based mutation analysis method, and applies specification-based mutation techniques for composite WS simulation and testing. Four categories of OWL-S mutant operators are specified, including data mutation, condition mutation, control flow mutation, and data flow mutation. Finally, the paper studies the ontology-based input mutation technique using a BookFinder service as a case study, which shows that ontology-based mutation provides viable test adequacy criteria for testing OWL-S specified composite WS.