This study aimed to analyze users' behaviors to use mobile services of academic libraries by indirectly observing users' experiences based on their diaries. Ultimately, this study intended to contribute to the development of mobile services in academic libraries by helping academic libraries understand users and their needs of mobile services. For this, diary method was conducted with 20 students at two academic libraries. These participants should report detailed process and thoughts immediately after using mobile library services at least once a day during a week. Totally 137 diaries were collected. And then this study conducted a content analysis to figure out what information needs they had, whether or not the needs were solved, what menu they selected, and what steps and gaps they got. In addition, on the basis of the findings, this study suggested further steps for improving mobile services at academic libraries.