In this paper, we present an approach to solve the problem of provably secure execution of semantic web service composition plans. The integrated components of this approach include our OWL-S service matchmaker, OWLS- MX, the service composition planner, OWLS-XPlan, and the security checker module for formally verifying the compliance of the created composition plan to be executed with given data and service security policies using type-based information flow analysis. We demonstrate this approach by means of its application to a use case scenario of health service composition planning.