Objective: This study aimed to systematically investigate whether anti-androgens could significantly reduce Obsessive-Compulsive Disorder (OCD) symptoms compared to placebo or usual care in OCD patients. Methods: PubMed, EMBASE, CENTRAL and International Clinical Trials Registry Platform (ICTRP) databases were searched up to October 2018 using relevant keywords. All randomized and if not available non-randomized studies conducted on a population including OCD patients who were administered with anti-androgen, which reported changes in their symptoms, were included. The studies on compulsive hypersexuality were excluded. Required data were extracted from full-text of the included articles by two independent authors. One randomized and four non-randomized trials were found. Results: The only randomized trial showed that flutamide, an anti-androgen agent, was effective in reducing compulsion scores in male OCD patients with comorbid Tourette syndrome, compared to placebo. Three out of four non-randomized trials showed that different anti-androgens including finasteride, cyproterone acetate and triptorelin were effective in reducing OCD symptoms. The only study, which failed to show the efficacy of an anti-androgen agent, administered OCD patients with flutamide. Despite the positive results, available studies provide the evidence with low quality based on the Grades of Recommendation, Assessment, Development and Evaluation Working Group (GRADE) approach. Conclusion: Available studies are not sufficient for a precise answer to our study question. There is still a need for further large randomized blinded clinical trials to evaluate the effectiveness of anti-androgens in OCD patients. It is recommended that gender, comorbidities and subscales of Yale-Brown Obsessive-Compulsive Score (Y-BOCS) should be considered in designing the studies and interpreting their results.