Objective: Based on findings of previous studies, those men on Methadone Maintenance Therapy (MMT) have a high prevalence of Erectile Dysfunction(ED), related to hypogonadism and depression. We conducted this study to evaluate the efficacy of Trazodone (an antidepressant which can improve sexual function) on this sexual dysfunction. Method: A structured interview was administered by the clinical staff.The interview contained questions about the subjects' socio-demographic characteristics, their drug use and sexual behavior.In addition to the socio-demographic survey, erectile function was assessed using erectile dysfunction (ED) intensity scale. Of the 157 subjects, 95 suffered from ED. The subjects were informed about the study. Then, seventy five patients voluntarily received 50mg of Trazodone for four days, and the dosage was increased to100 mg and maintained for 6 weeks. Fifty five patients who completed the treatment course were assessed by ED questionnaire again at the end of study. Statistical analysis was performed using Stata 8 software. Results: The prevalence of ED was 60.5% in our sample. The mean erectile dysfunction (ED) intensity scale was 12.21, and 16.78 before and after the treatment course respectively. (P<0.05)ED severity had no significant relation with age and type of substance dependency (P>0.05) ; but it had a significant relation with duration of Methadone therapy and Methadone daily dosage. (p<0.05) Conclusion: Trazodone may be effective in the treatment of methadone induced ED. Further studies with control groups and greater sample sizes are warranted.