Web services use an interoperable and loosely coupled data exchange architecture. Web services processing can cause significant runtime overhead, especially when the number of fine-grained transac- tions becomes large. Although some best-practice guidelines recommend coarse-grained messages to improve the performance of Web services, coarse- grained services may interfere with the componentiza- tion of the services. Service granularity should be designed for reusability and modularity. In this paper, we propose a SOAP message bundling framework. This framework enables bundling multiple messages into one message. With this framework, application developers do not have to consider the service granularity. Instead, the framework bundles some fine- grained messages into a single coarse-grained message. To support this framework, we provide for service providers (1) a WSDL conversion tool and (2) a skeleton wrapper generator. These tools let service providers receive bundled messages without modifying existing service implementations. We also provide (3) a stub wrapper generator that allows service requesters to use bundled services easily. The existing message exchanges are not influenced by this framework. We evaluated the performance gain in experiments using the Google SOAP API. The results showed that our approach improves the performance of Web services.