Web Services integration using languages such as BPEL is to be applied not only on the Internet but also in pervasive networks using wireless mobile devices. However, in such a network it is necessary to deal with constraints in resources, typically the relative narrowness and instability of network connections. Our study adopts the mobile agent technology in response to this problem and presents a mobile agent system for Web Services integration. In our system, the physical behaviors of mobile agents, including migration and cloning, are separated from the integration logic and are described as simple rules added to the BPEL integration process description. This makes it possible to add or change physical behaviors according to the environmental conditions without modification of the BPEL description.