The paradigm of Web services that transforms the Internet from a repository of data into a repository of services has been gathering significant momentum in both academia and industry in recent years. However, as more and more Web services are published on the Internet, how to choose the most appropriate Web service components from the sea of ever-changing, unpredictable, and largely uncontrollable Web services poses a big challenge. In this paper we propose a mobile agent-based approach that selects reliable Web service components in a cost-effective manner.