This research aims at deepening the understanding of the effects of information systems on supply chain operations, and to find the level and direction of the relationship between Enterprise Resource Planning (ERP) and Knowledge Management (KM) in the context of operational and financial performance. Essentially, this study emphasizes the explanation of the complementary relationship between ERP and KM. Therefore, the mediating effect of KM is also analyzed. Using a survey method, 163 responses are collected from Turkish manufacturing companies which operate in a variety of industries. A structural equation modelling (SEM) is used to test both the reliability and validity of measurement and the structural path model. The results show that ERP has no significantly positive effect on operational performance, but it is a precedent of KM. Moreover, results also show that KM affects operational performance positively and it has a mediating effect for the relationship between ERP and operational performance. Lastly, the path analysis shows that operational performance is positively associated with financial performance.