The Web service composition can be defined as the process of combining existing services to produce new ones. Indeed, composition to develop higher-level services, so-called composite services, by re-using existing services is Service Oriented Architectures (SOA) core capability. For this purpose, languages such as BPEL and platforms like the orchestration engine appeared for the specification and the implementation of service compositions. However, the expressiveness of these languages deals only with functional compositions and does not take into account the composite Web services properties validation and the tools associated to these languages do not support simulation of behavioural requirements. Our contribution consists in using software agents to provide a simulation tool to BPEL, to observe agents behaviours and to evaluate properties. Simulation plays an important role by exploring ”what-if” questions during the process composition phase. The proposed approach is implemented using JADE platform.