Objectives: Obsessive-compulsive disorder (OCD) is defined in the diagnostic and statistical manual of mental disorders, 5th Edition (DSM-5) as annoying and unpleasant thoughts or images (obsession) associated with repetitive and unwanted actions (compulsion). This study aims to compare emotional schema therapy augmented exposure and response prevention (ESTERP) with exposure and response prevention (ERP) and pharmacotherapy in improving the symptoms of OCD patients. Methods: This was a randomized clinical trial study. The participants included all patients with OCD who were referred to hospitals and clinics in Tehran, Iran. A total of 45 patients with OCD were selected through purposeful sampling, of which 15 patients were randomly assigned to the ESTERP group, 15 to the ERP group, and 15 to the pharmacotherapy group. After randomly placing the patients in the three groups, all patients completed the Yale-Brown obsessive-compulsive scale-2nd edition (Y-BOCS-II), the four systems anxiety questionnaire (FSAQ), and the Beck depression inventory-2nd edition (BDI-II) before, in the end, and 2 months after the treatment. Then, the data were analyzed using nonparametric tests and the reliable change index. Results: There was a significant difference between the treatment of ESTERP with ERP and pharmacotherapy in the symptoms and severity of OCD and anxiety (except for the depression variable) in patients with OCD. In addition, the findings of the clinical significance of ESTERP compared to the other two treatments showed more significant changes in symptoms and severity of OCD and depression (except for the anxiety variable). Conclusion: Both ESTERP and ERP treatments are effective in patients with OCD and both lead to more improvements in patients’ symptoms than pharmacotherapy.