Knowledge sharing is the most important issue in the knowledge management. In this study, we mainly refer the IPO model to explore the mediating effect of knowledge sharing among these factors that influencing information system development (ISD) team effectiveness. Using hierarchical regression analysis, this study analyzes data from 35 ISD teams. The results indicate that self-efficacy, team interaction, and team member trust of team trust, all have significant effects on knowledge sharing. Furthermore, it appears that knowledge sharing plays mediating roles among self-efficacy-team effectiveness, team interaction-team effectiveness, and team trust-team effectiveness. Therefore, we suggest that managers should encourage team members to share knowledge each other.