Web services have emerged as a key technology that enables interoperability between distributed applications. It is desirable that SOAP, being the Web service transport protocol for inter-connecting applications across organizations, performs efficiently in environments where there are a large number of transactions. This paper presents a novel approach to address this issue and hence improve Web services performance. We propose a similaritybased SOAP multicast protocol (SMP) that reduces the network load by optimizing the generated traffic size. In particular, SMP reuses the common template among the SOAP messages and only sends one copy of the common part to multiple clients. The results obtained from our experiments indicate that SMP achieved a 75 percent reduction in network traffic compared to traditional SOAP unicast.