In recent years, Web services have been drawing more attention to the computer industry. They are built on open standards and provide solutions for integrating applications across enterprises. The technologies behind Web services are Universal Description, Discovery and Integration, Web Services Description Language and Simple Object Access Protocol (SOAP). SOAP, which is responsible for delivering messages between applications, is a connectionless protocol. In other words, SOAP cannot keep the session state between SOAP calls. However, most Ecommerce applications need to maintain the session state and transaction information between Web services. This paper proposes and develops a new mechanism that supports Web services session management by using Session Initiation Protocol which is an IETF standard session control protocol. In addition, based on this session management mechanism, a simple transaction management solution for Web services is proposed. Two systems are implemented as demonstrations for both mechanisms in this paper. Moreover, more functions can be added in these systems, such as security, service registry and discovery.