Increasingly, companies are outsourcing complex IT projects to offshore locations. Such globalization trend has led to challenges for both clients and vendors. The objective of this research is to enhance our understanding of offshore IS development project success from the lens of knowledge sharing. From the vendor's perspective, we investigate the mediating role played by knowledge sharing in the success of offshore software development and identify factors that contribute to knowledge sharing in offshore software development. A survey method was used to collect data in China and validate the research model. Our findings confirm that knowledge sharing mediates the impact of the use of methodology and relationship with clients on the success of offshore software development projects; particularly, knowledge sharing has more impact on process efficiency than on product quality. This study contributes to the theoretical understandings on how development methodology and vendors' relationship with clients help overcome the challenges in off shoring software development (OSD), and how knowledge sharing functions as a mediator between these factors and success of OSD. The findings also help vendors identify critical determinants of knowledge sharing in OSD and suggest strategies to execute OSD.