Changes in recent business and scientific environment have created a necessity for more efficient and effective workflow infrastructure. With increasing emphasis on Service-oriented architecture, service composition becomes a hot topic in workflow research. This paper proposes a novel approach of using ECA rules to realize the workflow modeling and implementation for service composition. First of all, the concept and formalization of ECA rule-based workflow is presented. Special activities and data structures are customized for the purpose of service composition. Second, an automatic event composition and decomposition algorithm is developed to ensure the correctness and validness of service composition at design time. Finally, the proposed ECA rule-based approach for service composition is illustrated through the implementation of a workflow prototype system.