This study examines the compatibility of acceptance and commitment therapy (ACT) with religious aspects of scrupulosity and evaluates it in a case study. A mixed-method was used to comply with the intervention protocol; qualitative and quantitative study. In the qualitative section, religious sources were used to examine verses and hadiths' formal and content validity. Then the verses were extracted, and narrations related to ACT components were given to experts by the Delphi method. In the next step, CVI and CVR of verses and narrations were obtained, after that the adapted model based on Twohig's (2004) protocol in 22 to 25 sessions was used. In this stage, a "case study" from April 2020 to September 2020, as a quasi-experimental pre/post test with the sample at convenience, was considered and implemented on an Iranian patient with scrupulosity. The client received treatment. For evaluation, the Yale-Brown Obsessive-Compulsive Disorder Scale (Y-BOCS), the Beck Depression Inventory-II, the Performance Scale (WHODAS 2.0), the Kugler and Jones Guilt Feeling Inventory, Penn Scrupulosity Questionnaire, and Religious Beliefs Questionnaire was used. We compared the total score of the pre-tests and post-tests. The outputs showed that the severity of the symptoms of obsessive-compulsive disorder has decreased, and the scores of other questionnaires have decreased. Treatment process acceptability was high. The results showed that ACT with the religious aspects has good efficacy.
