Introduction: Library websites are one of the main ways to access to library resources, therefore, they should be desihned according to users' needs to ensure their proper performance. This study aims to evaluate the usability of central libraries websites of Top Iranian Medical Universities and determinate its relationship with webometric ranking.
Methods: This descriptive-analytical, cross-sectional study was conducted in 2013 to evaluate the usability of central libraries’ websites of Iranian Medical Universities, type I (Tehran, Shahid Beheshti, Isfahan, Shiraz, Tabriz, Mashhad, Ahvaz, Kerman, Mazandaran, Uromia, Kermanshah and Zanjan). Three evaluators independently examined the websites using Nielsen’s usability principles. Then a list of usability problems was identified and classified based on their severity. Then, the correlation between the ranking of the central library websites and the ranking of webometrics was determined. Spss20 was used to analyse the data.
 Results: according to the findings, the highest number of problems was related to "flexibility and efficiency of use" and the lowest was related to "error prevention". Based on the severity of identified problems, the highest number of problems were "major" ones. There was no significant correlation between the usability ranking of the central library websites and the webometrics ranking of the same universities.
 Conclusion: Despite the wide usage and variety of users, library websites interfaces are not of good usability, therefore, it is recommended to to consider standards and principles while designing websites.