A significant number of information system development (ISD) projects fail to achieve their predefined goals on time and/or within budget. Many organizations recognize that users can engage in projects to minimize the difficulties in effectively controlling the project and maximize the value created; therefore, user co-production is a crucial for organizations to enhance the effectiveness of ISD project. This study attempts to understand the antecedents and consequences of user co-production in ISD project. As a key contribution, we posit that user co-production is influenced by social capitals between users and developers. We then postulate that user co-production determines the project outcomes, which are shaped by system quality, user satisfaction and project performance. Data were gathered from a questionnaire survey of 103 pairs of user representatives and developers. Our results show that project outcomes are significantly influenced by user co-production. Furthermore, social capitals between user representatives and developers have positively significant influence on user co-production.