Erectile dysfunction (ED) due to androgen deficiency is rare in the young population. We retrospectively evaluated in this study men aged 18-40 years presenting with ED from 2015 to 2017. The International Index of Erectile Function-5 (IIEF-5) and Erection Hardness Grade Scores (EHGS) were used to assess erectile function. Total testosterone (TT), sex hormone-binding globulin (SHBG), lipid profile, and glycometabolic indicators were tested in fasting blood sample. TT and SHBG were detected by electrochemiluminescence immunoassay, and free (FT) and bio-available testosterone (BT) were calculated from a validated formula. Linear regression was used to analyze the data. In total, 140 cases (30.56 +/- 4.81 years) with a mean TT levels of 6.15 +/- 2.17 ng/ml were enrolled. Decreased levels of FT were associated with lower IIEF-5 scores(beta = 0.176, P = 0.048) and EHGS (beta = 0.198, P = 0.026) after adjustment for age, body mass index (BMI), smoking, comorbidities, high-sensitive C-reactive protein (hsCRP), uric acid, fructosamine, and quantitative insulin sensitivity check index (QUICKI). TT was only associated with EHGS in the crude model (beta = 0.177, P = 0.037) and some single factor adjustment models, whereas BT and SHBG were not related with erectile function in any model. Low FT level, even in the presence of normal TT, is associated with ED severity in young men. FT levels should be screened in ED patient even with normal total testosterone.