["Child and Adolescent Mental Health, EarlyView. ", "\n\nBackground\nObsessive‐compulsive related maladaptive beliefs play an essential role in the development and maintenance of obsessive‐compulsive disorder (OCD). Nevertheless, there is a lack of accessible and widespread strategies capable of challenging such beliefs in the youth general population. This study aimed to assess the efficacy of a mobile health tool (GGOC‐AD) in reducing maladaptive OCD beliefs and symptoms in Spanish community adolescents and explore its impact on emotional symptoms and self‐esteem.\n\n\nMethods\nA two‐armed parallel randomized controlled trial (https://clinicaltrials.gov/study/NCT06033391) was carried out with 94 students (Mage = 15.09 (SD = 0.6) years; 69.1% girls). Participants either used GGOC‐AD, a nonguided mobile intervention targeting maladaptive OCD beliefs (experimental group; n = 48), or GGN‐AD, an active comparator with neutral content (control group, n = 46) over a 14‐day period. Assessments were conducted at baseline (T1), immediately postintervention (T2), and 1 month later (T3). A mixed effects model for repeated measures (MMRM) was conducted to evaluate the effects on maladaptive OCD beliefs and symptoms, emotional symptoms, and self‐esteem. The outcome was specified as the scores in both T2 and T3.\n\n\nResults\nCompleting GGOC‐AD was associated with statistically significantly lower maladaptive beliefs related to responsibility and threat estimation (Estimate [SD] = 3.62 [1.47]; p = .014; d = 0.30), perfectionism and intolerance of uncertainty (Estimate [SD] = 3.07 [1.34]; p = .022; d = 0.24); and importance and need to control thoughts (Estimate [SD] = 4.34 [1.17]; p > .001; d = 0.48); and statistically significantly lower OCD symptoms (Estimate [SD] = 2.57[0.81]; p = .001; d = 0.34), compared to completing GGN‐AD. No differences between groups were observed in emotional symptoms and self‐esteem.\n\n\nConclusion\nGGOC‐AD appears to be a promising tool for addressing OCD risk factors and enhancing adolescents' mental well‐being.\n\n"]