Moringa oleifera (MO) is an excellent source of dietary antioxidant. MO is used traditionally to enhance libido and as an aphrodisiac in the treatment of sexual dysfunction. This study aimed to investigate the direct effect of aqueous leaf extract of MO on Leydig cell in vitro. Specifically, the effect of MO on viability, testosterone production, antioxidant activity and lipid peroxidation on TM3 cells were evaluated. TM3 cells seeded for 24 hr were exposed to aqueous leaf extract of MO (0, 10, 50, 100, 250, 500 and 1,000 µg/ml) for 24 hr, in the absence or presence of human chorionic gonadotropin (hCG; 6 mIU/200 µl). Cell viability remained unchanged while testosterone production significantly increased at 500 and 1,000 µg/ml of the extract under stimulatory conditions by 34 and 45% respectively. Glutathione level substantially increased at 250 µg/ml, while lipid peroxidation, catalase and superoxide dismutase activity, and total antioxidant capacity remained unchanged. Our results demonstrate the androgenic effect of MO especially at high concentrations in TM3 cells. The androgenic effect may be attributed to its antioxidant enzyme activities.