Considering that the amount of money spent for implementing digital library is very high, it is therefore very crucial to evaluate its effectiveness. Since the implementation of digital library in the University of Tehran, Iran, no attempt has been made to evaluate its effectiveness. Against this concern, a study was carried out to investigate the effectiveness of the digital library from the user perspective. Building upon the Information Systems Success Model, this study measured digital library use and its corresponding determinants and impacts. Adopting the survey research methodology involving 425 students, the findings suggest that three library characteristics, namely, information quality, systems quality and service quality are predictors of digital library use. In addition, the findings also indicate that the degree of digital library use is impacting the user satisfaction and their personal sense of accomplishment.