Abstract: One crucial issue of service-based trustworthy application development is how to measure the trustworthiness of Web services. A comprehensive trustworthiness measurement model for Web services, TMM4WS, was proposed based on the unique features of Web services. The model measures the trustworthiness of a Web service in terms of both its source code and external usage. A tool called TMT4WS was developed to support the model. An empirical study was conducted on tens of Web services to validate the effectiveness of the model and its supporting tool. Experimental results show that the model and its supporting tool can be employed to provide a quantitative trustworthiness measurement of Web services.