In knowledge-intensive business service, the participation of clients is important to service providers to successfully deliver high-quality service. Our research discusses this topic in enterprise system (ES) service, where clients’ co-production behavior and citizenship behavior are critical because they need to provide specific business knowledge to vendors to develop a satisfactory ES. However, because clients are unaware of vendor’s competence and goodwill, the potential risk impedes them from performing such behaviors. As information asymmetry exists between vendors and clients, we adopt signaling theory to investigate how to improve clients’ co-production behavior and citizenship behavior. According to this theory, we consider vendor’s in-role and extra-role performance as the signal sent to clients, which influence clients’ trust in vendor’s competence and goodwill. This trust leads to co-production behavior and citizenship behavior as a consequence. The current study intends to conduct questionnaire survey among clients of a focal ES vendor. Expected contributions are specified at the end of this paper.