Mental status examination is an important stage in the assessment process because it serves as the foundation for establishing nursing diagnosis and intervention. Until now many students still feel difficult to understand the terms in the assessment of mental status. Interactive Mobile Learning in one of the media that is currently being developed. The use of this media will provide more in-depth learning opportunities, and students can practice their skills in carrying out practicals because of the mobility principle possessed by smartphones. The purpose of this study was to develop a smartphone-based app and evaluate the app's effectiveness by measuring nursing students' knowledge of mental status examination. Design: A randomized trial with a pre-and post-test design was conducted at a university in Indonesia. A total of seventy junior nursing students participated in this study. The intervention group received a smartphone-based app, and the control group received one-time lecture-based learning. We offered the experimental group the app and information about how to use it, and we encouraged them to use it. The control group received classroom instruction. Results: The intervention group scored significantly higher than the control group on knowledge score (t = 19.40, p = 0.000) and satisfaction with the learning method (t = 0.640, p = 0.021) Conclusion: These findings suggest that smartphone-based education could be an effective method in nursing education for teaching mental status examinations.