BACKGROUND: Self-help programs without therapist involvement for obsessive-compulsive disorder (OCD) are promising, but the high dropout rate is a significant issue. Our software, which incorporates entertainment elements, showed a completion rate of over 80% in a pre-post comparison study, with superior effectiveness. This is the protocol for a study that aims to evaluate the efficacy and tolerability of a video-based mobile application for OCD treatment through a randomized controlled trial. METHODS: This study is designed as a randomized controlled trial with two parallel group comparison, with assessors blinded to group allocation. The study will include outpatients aged 18 years or older diagnosed with OCD. The intervention group will receive a mobile-device-based intervention using an application grounded in cognitive behavioral therapy. The treatment period will be 8 weeks, during which 21 sessions will be conducted. Participants not allocated to the intervention group will be assigned to a waitlist control group for 8 weeks. The primary outcome for effectiveness will be the comparison of the Yale-Brown Obsessive Compulsive Scale. As the primary outcome for tolerability, participants in the intervention group who complete 80% or more of the sessions by the 8-week point will be defined as treatment completers, and the proportion of completers will be calculated. Assuming a 10% attrition rate, a total of 88 participants will be needed. RESULTS: Results will be presented according to the protocol. CONCLUSIONS: If this study demonstrates that OCD can be improved through mobile-based self-help treatment without therapist involvement, it will become an important treatment option for patients.