Introduction: Stigmatizing attitudes is a problem associated to mental disorders. In obsessive-compulsive disorder (OCD) stigma has been associated to shame, guilty and delay asking for help. Objective: To present the design of a mobile health application (app), named EsTOCma, with the objective to increase OCD mental health literacy, help seeking attitudes, and reduce stigmatizing/ self-stigmatizing attitudes and social distance associated with OCD in adult population (non-clinical and OCD population and their relatives). Method: Method: The requirements have been developed based on a literature review on mental health antistigma interventions, OCD stigma research, and serious games research. Focus group with PhD-level clinical psychologist and interviews with a usability expert were made to complete the APP specifications. Results: esTOCma is a game in which participants are asked to fight against the OCD stigma monster through ten missions along 8-10 days. It is organized into three levels that involve a different methodological approach: Psychoeducation, Contact and Cognitive Restructuring respectively. The first one provides participants with general information about OCD, the second one brings participants closer to a more realistic view of the disorder through indirect contact of people with OCD, and the last one aims to replace possible dysfunctional beliefs about OCD and characteristics of OCD patients. Discussion: It is expected that by increasing knowledge and reducing stigmatizing attitudes, esTOCma will improve access to mental health services and, therefore, reduce the personal and financial costs of OCD. Acknowledgments: Ministerio de Ciencia, Innovación y Universidades (Spain) [RTI2018-098349-B-I00].