OPAC is a very important interface for user to use and search library collection and electronic resources. The purpose of this study is to analyze empirically the impact of OPAC usability on user satisfaction and loyalty in an university library setting. The OPAC functions investigated are keyword searching, integrated searching, faceted navigation, relevance ranking, spelling check, recommendations, user participation, and Really Simple Syndication(RSS), etc. This study investigated what usability effects on user satisfaction and loyalty and suggested the way to improve user satisfaction and loyalty.