Background: erectile dysfunction (ED) is the persistent inability to attain or maintain an erection. ED affects millions of men worldwide. The pathophysiology of ED includes vasculogenic, neurogenic, hormonal, anatomical, drug-induced and psychogenic causes. Endothelial dysfunction (EDys) is an important pathophysiologic factor underlying vasculogenic erectile dysfunction. The pathogenesis of both EDys and ED are linked through decreased expression and activation of endothelial nitric oxide synthase (NOS) which is responsible for formation of Nitric Oxide (NO). NO is a relaxing factor which plays a major role in activation and maintenance of the erection process. Aim of the work: this study aimed to detect the possible relationship between serum folic acid and erectile dysfunction by measuring serum FA concentration in patients with erectile dysfunction and comparing them with the healthy controls. Methodology: our study has been carried out on 90 individuals who were categorized into two groups. Group 1: 60 married males complained of ED. Group 2: 30 married potent males as a control.All participants were subjected to : personal history, past history of medical diseases and operations, sexual history, general examination, genital examination and evaluation of erectile function according to the International Index of Erectile Function (IIEF-5) Questionnaire). Fasting serum samples were collected from all participants and assayed for serum total testosterone, serum prolactin, serum cholesterol, serum triglycerides (TG), HbA1c and serum folic acid.Results: results of the current study showed a significant relation between folic acid and ED. FA level was declined as ED severity increased. It is thought that ED severity was related to HHcy which was related to the severity of FA deficiency.Conclusion: a significant association between serum FA level and ED severity was detected in the current study. Serum FA level decreased as the severity of ED increased. These results suggest that FA deficiency might reflect the severity of ED. Recommendations: serum folic acid assessment as a part of the routine investigations for patients complaining with erectile dysfunction. Additional experimental and clinical studies are needed to determine whether FA supplementation may be beneficial for patients having ED.