The purpose of this study is to present a theoretical framework and practical methodology to extend the scope of Library and Information Science by incorporating the usability evaluation of e-book, which has considerably increased in proportion in the digital library. By sirveying e-book users and through statistical analysis. it was found that rebuilding a set of usabllity evaluation factors for e-books is necessary to activate e-books in the digital libraries. This study inclusively presents a conceptual model of e-book usability evaluation and suggests guidelines for usability principles.