Objective: In order to ensure the successful implementation of a nursing information system (NIS), nurses and nursing students must be adequately trained. In order to do this effectively, it is essential to understand their training needs. This study focuses on the training needs of nursing students in particular through the identification of the usage problems they encounter. Usability testing, which involves observing users' interaction with an NIS, overcomes the deficiencies of traditional approaches of training needs analysis such as interview and survey. The study applied usability test to assess training needs of nursing students to learn to use a specific NIS, the "Care Planning Assessment Tool" (CPAT). Methods: An experiment in which novice CPAT users were expected to learn to use the software through task-based exploration was conducted. Eight nursing undergraduate students who had never used the software were recruited. Participants' interactions with the system were captured by screen capture software. Meanwhile, participants' "think aloud" verbal expression of their usage problems was audio-taped. Results: A coding scheme was used in analysing the captured audio and video data. Ten common usage problems were identified. From these problems, three areas of knowledge gap that this cohort of novice users experienced were identified. Conclusion: The training needs of nursing students learning to use an NIS was conceptualised in a model consisting of three types of knowledge, i.e. computer skills, knowledge about the NIS and knowledge about procedure of nursing documentation. The knowledge gap must be filled in order to ensure effective training.