In this study, we present a theoretical model of motivations explaining the relationship between reputation system and knowledge contribution in online communities. Knowledge contribution is modeled as a response to varied motivations (base on Maslow’s hierarchy of needs). These motivations are proposed to be influenced by the availability of reputation systems. We test this model in an experiment. Given the importance of global knowledge sharing in today’s world, we expect our findings will be useful to inform the design of online knowledge-sharing communities.