Web Services Composition(WSC) is becoming an important approach to EAI and its reliability needs to be guaranteed by introducing the transaction mechanism. WSC transactions differ from traditional transactions in that they execute over long periods and cross multiple loosely-coupled organizations, so traditional transaction processing mechanism is inappropriate for them. This paper summarizes the characteristics of WSC transaction and presents its multilayer framework, and then analyses the coordination procedure of WSC transaction in the framework, and finally gives its coordination protocol and designs a prototype system for WSC transaction.