With regard to the potential of huge knowledge dissemination by academic library websites, their usability is considered as a matter of great interest to university administrators as well as users. In the present study, a descriptive survey was designed aimed at evaluating usability of central library websites of type-1 universities of medical sciences in Iran in order to identify their usability issues and to provide inputs for possible remediation efforts to improve the design of similar websites in the future. The research procedure involved a library study to identify the tasks typically needed on library websites, use of the identified tasks to design a checklist for measuring three dimensions of usability (effectiveness, efficiency, and satisfaction), and finally a usability evaluation by two specialists of medical informatics and two librarianship experts. The given websites were rated “good” (60 % - 80 %) in terms of usability and no statistically significant difference was found between evaluations by different experts. It was concluded that more attention to website usability could improve users’ interest in services and facilitate realisation of goals in parent organisations. The results of this study could provide a basic framework for website design and improvement through giving proper attention to usability dimensions.