Indonesian government institutions have become more aware of the importance of knowledge management for improving organizational performance. Development Planning Agency of Southern Sumatera Province (Bappeda Sumsel) is a government institution who implemented a Knowledge Management System called Online Disposition Website. Unfortunately, the system has not been used optimally as the rate of disposition letters produced by the system is less than one percent throughout the year 2016. In this paper, we focus on finding the affecting factors of KMS implementation in Bappeda Sumsel. A survey was spread to 123 employees in Bappeda Sumsel. The research model was adapted from six latent variables of information system success model by DeLone & McLean. We empyol structural equation model to analyze survey result. We found that there is positive influence from system quality and service quality to kms use. Also, we predicate that there is positive influence from knowledge quality, service and KMS use to user satisfaction. Additionally, we found that there is positive influence from kms use dan user satisfaction to net benefit. Success model as a critical part for knowledge management system is analyzed to make sure knowledge management system is well implemented and used by the users.