BACKGROUND: Obsessive-compulsive disorder (OCD) is a disabling disorder, and self-stigma negatively impacts quality of life, symptom severity and self-esteem. esTOCma is a smartphone-based serious game developed to increase knowledge about OCD and reduce stigma. It features 10 missions using psychoeducation, indirect contact and cognitive restructuring. Players help 10 characters escape the OCD stigma monster. AIMS: To explore, in individuals with a self-reported diagnosis of OCD, the feasibility, acceptability and preliminary effectiveness of esTOCma to change self-stigma and knowledge about OCD, OC severity, guilt, quality of life and self-esteem. MATERIALS AND METHODS: A single-arm pilot study with 130 participants who completed esTOCma and pre-, post- and 3-month follow-up assessments. RESULTS: Half of participants spent 9-10-days playing with the app and most of them found it useful/very useful and easy to use. Self-stigma was associated with higher OC symptoms, guilt and lower quality of life, self-esteem and knowledge about OCD. After using the app, participants showed lower levels of self-stigma, OC symptoms and guilt, and higher levels of quality of life, self-esteem and knowledge about OCD. Changes were maintained or increased at a 3-month follow-up. DISCUSSION: esTOCma is a feasible and acceptable app that could help people with OCD to increase their knowledge and understanding of the disorder, dismiss self-stigma and OC symptoms, and at the same time increase self-esteem and quality of life. A replication of the study with a control sample is needed to validate our findings. CONCLUSION: Tools like the esTOCma app, accessible 24/7, offer a means to tackle self-stigma detrimental effects.