In order to evaluate and estimate the success of knowledge management systems it is necessary to define performance measurement indices. Considering this importance area a research has been done to measure the efficiency and effectiveness of knowledge management systems. In addition the issue of how to assess the impact of knowledge management on organizational performance has been studied. Based on the research and reviewing the relevant literature in this paper a model has been presented for measuring performance of knowledge management systems. Using this model a number of indices are introduced and their interrelations are explained. At the end this paper also suggests some research areas in the field of performance measurement of knowledge management implementation.