In order to investigate the effects of molybdenum (Mo) on sperm parameters and testicular oxidative stress, the ICR strain of adult mice were exposed to different doses of molybdenum for a sub-acute toxicity test.Compared to control, our results showed that the sperm parameters, including the epididymis index, sperm motility, sperm count and morphology, were improved by a moderate dose of Mo (25 mg/L), but were negatively affected at high doses (≥ 100 mg/L).In addition, the changes of sperm parameters were accompanied with the changes of the superoxide dismutase (SOD) activities, the glutathione peroxidase (GPx) activities, and the malondialdehyde (MDA) levels in testes.In conclusion, molybdenum affects the sperm quality through regulating the testicular oxidative stress in a parabola-shape manner.This study indicates that the Mo can improve male reproductive functions at a suitable concentration, and it might be a novel drug candidate for the treatment of male infertility.