Background and Objectives: Mental disorders, including obsessive-compulsive disorder, are multidimensional phenomena. Most patients with mental disorders reject or resist receiving treatments and hence, effective strategies are needed for their treatment.As an extension of cognitive behavioral therapy, schema therapy incorporates different views and presents a multi-component approach for the management of not only cognitions and behaviors, but also emotions. This study aimed to assess the effects of schema therapy on emotional self-awareness, vulnerability, and obsessive symptoms among patients with obsessive-compulsive disorder. Methods: This was an experimental clinical trial. Study population consisted of all patients with obsessive-compulsive disorder who, in a six-month period in 2016, referred to psychology clinics located in Birjand, Iran. A total of 32 eligible patients were recruited and randomly assigned to control and intervention (i.e. schema therapy) groups. Data collection instruments were a researchermade demographic questionnaire, Young schema questionnaire, and Yale-Brown obsessive-compulsive scale. The data were entered into the SPSS software (v. 22.0) and analyzed using the multivariate analysis of covariance at a significance level of less than 0.05. Results: One patient from the intervention group voluntarily withdrew from the study. The posttest mean score of emotional selfawareness in the intervention group was significantly greater than the pretest mean score, while the posttest mean scores of the vulnerability schema and obsessive symptoms were significantly lower than the pretest scores (P < 0.001). Moreover, the control and the intervention groups differed significantly from each other respecting the posttest mean scores of emotional self-awareness, vulnerability, and obsessive symptoms (P < 0.001). Conclusions: Schema therapy alleviates obsessive symptoms through positively affecting emotional self-awareness and the two schemas of vulnerability. These findings suggest that these variables play significant roles in the development of obsessive symptoms. Therefore, schema therapy is recommended as an effective treatment for outpatients suffering from obsessive-compulsive disorder.