Online user collaborative innovation (co-innovation) community is increasingly used to involve customers in product and service innovation. Why users participate in the innovation is a critical problem for firms managing the community. However, little is known about user motivations. The purpose of this paper is to identify the motivations for users participating in online co-innovation communities. Based on the expectancy theory, this study employs netnography to investigate user motivations with user actual participation behaviors. In accordance with the procedures of netnography, user participation data is collected though web mining. Then, four behavior properties are defined according to behavior characteristics. Finally, six different motivations are identified. The results show that a small number of users are inspired by status and reputation and individuality demands. Monetary rewards is one of the main motivations that make users contributing to the complex technical product process. Social relations and interest and curiosity are also important factors that drive users participating. The most of users partake for interest and curiosity. According to the different motivations, this study provides several managerial insights on how to successfully attract and motivate more users to contribute to product development in co-innovation communities. This paper contributes a systematic and efficient method for identifying user motivations. In addition, the study provides a better theoretical understanding of user motivations and offers practice guidance on inspiring and managing users for co-innovation community practitioners.