Background: Erectile function may be secondary to much systemic illness, both physical and psychological, and is a well-documented side effect of prostatic cancer treatment. Objective: To asses effect of folic acid supplementation on homocysteine plasma level in either peripheral and penile blood before among vasculogenic erectile dysfunction patients. Patients and methods: This study included 22 Egyptian patients ranged from 30-60 years old with vasculogenic ED proved by penile duplex ultrasound. All patients subjected to penile Duplex ultrasound, peripheral and penile blood samples were for plasma homocysteine concentration evaluation before and after oral folic acid 500 mcg per day for 3 months. Results: There was statistically significant difference between either peripheral or penile homocystiene before and after. There was a significant increase in peak systolic value (PSV) after the treatment than its value before the treatment. Also, the end-diastolic velocity (EDV) before therapy was significantly higher than its value after therapy. There was a significant increase in international index of erectile Function-5 questionnaire after the treatment (15.5±3.3) than its value before the treatment. Conclusion: There was a significant relation between Hcys and either ED or penile arterial flow. From these results, Elevated plasma Hcys level was considered as independent risk factor for ED.