Recently WOM has become popular with the penetration of Internet and the popularity of social media, andattracted the attention of IS researchers. This study develops a model to explore the factors motivating e-service users’ WOM behavior from the expectation confirmation paradigm together with trust. The research model was empirical tested with 543 valid responses from the online travel service users. The research results indicate that perceived usefulness and user satisfaction affect e-service users’ WOM behavior positively together with trust. Perceived usefulness was found to exert the strongest influence on WOM than satisfaction and trust. The implications to theories and practice are discussed as well.