This study tried to evaluate the usability of web-based academic library services delivered to users in terms of effectiveness, efficiency, and user satisfaction. 13 subjects were randomly selected on the voluntary basis in Duksung Women's University Library from Dec. 15, 2001 to Feb. 27, 2002. They were given six kinds of tasks related to the use of library services through the library website. 3.6 tasks out of 6 were given right answers by subjects, with success rate of 60% and average spent time of 2 minutes and 22 seconds. The most effective library services on the website was a book search with success rate of 100%. However the least effective service was journal article search with success rate of 23.1% . The most efficient library service on the web was a book search. 100% of subjects found the answer in 42.2 seconds, while the least efficient library service was journal article search in which 23.1% of subjects found the answer in 271.7 seconds. Subjects were highly satisfied with the book request service on the web since it is the easiest to understand and the most convenient to use.