Open Source Software is becoming evermore important and widespread these days, so its maintenance has become important issue. In this paper, we presented an evaluation framework for Open Source Software maintenance. The framework was evaluated with five well known case studies. The results showed that our framework was suitable for evaluating scale of the project and activity, efficiency, traceability and quickness of the defect management and maintenance processes. The case studies showed that quality of the defect reports was low and therefore many of them were ignored as duplicate or invalid. In addition, most of the software changes were not connected to defects, which may express lack of management.