This article demonstrates the way in which Knowledge Management System (KMS) quality influences effective competitive advantage through decision making and through organizational learning. The results indicate strong support for the research model consisting of the independent variable (KMS Quality) and the dependent variables (decision making, organization learning capability and competitive advantage). The model explains respectively 45% of the decision making, 41% of the organization learning capability and 78% of the competitive advantage variance. It concludes that KMS quality plays an important role in sustaining competitive advantage. In light of these findings, implications for theory and practice are discussed.