Metasearch systems perform simultaneous searches across heterogeneous electronic resources through a single entry. In order to serve users, more and more libraries install metasearch systems to integrate their resources. This study aims to investigate the usability of MUSE Search, the metasearch system installed in the National Taiwan University Library, and to better understand user viewpoints toward this system. Five components of usability were analyzed: efficiency, effectiveness, learnability, engagement, and error. Observations and interviews were conducted in this study. Ten graduate students from the fields of humanities, social science, nature science, life science, and engineering science were solicited in the study. Students were requested to achieve four tasks. While they searching through MUSE Search, a researcher observed their behaviors and took notes. After the tasks were completed, students were interviewed by being asked questions concerning the usability of MUSE Search. Their comments and satisfaction levels were also collected. The conclusions were divided into five components of usability. According to the findings of this study, suggestions concerning MUSE Search are as follows: 1. to revise improper display of information in MUSE Search. 2. To add new search functions, or revise old ones to meet user needs. 3. To improve help functions. 4. To revise terminologies which are difficult to be understood.