Institutional repositories are “digital collections that capture and preserve the intellectual output of universities” (Crow, 2002). While still in their initial stages of development, much attention has been paid to the technical and administrative components. This paper examines the usability of the interfaces of two of the most commonly used institutional repository systems: DSpace and Eprints. By using heuristic evaluation and usability testing, eighteen undergraduate students were tested using a between subjects experimental design. Measures included time for completing tasks, the number of errors, and users’ satisfaction from post-test questionnaires. Results of the study indicated that DSpace users spent less time completing tasks and made fewer errors than Eprints users. Overall satisfaction of DSpace was also higher than Eprints. Based on this analysis of problem areas, the study suggests guidelines for institutional repository interfaces.