The U-library service is a user-oriented library service through which users, after browsing and making reservations using the Internet and smartphones, can borrow and return library materials at an unmanned circulation system located in places, such as subway stations, without visiting the library. However, the U-library service is still in the early stages both quantitatively and qualitatively. In that, this study, in order to enhance our understanding of the U-library service, conceptualizes the unmanned circulation system, investigates current situation by examining and analyzing some U-library service cases, and pinpoints some problems while making some suggestions for improvement.