Manganese (Mn2+) is a chain-breaking antioxidant in biological systems. The objective of the present study was to determine the optimal dose of Mn2+ to reverse free radical-mediated oxidative damage on motility, viability, and lipid peroxidation (LPO) of sperm from five bulls (local crossbred cattle). Fresh semen was suspended in 2.9% sodium citrate, divided into equal fractions, and subjected to Mn2+ treatment (0, 60, 100, or 200 µM) in the presence or absence of an oxidative stress inducer (ferrous ascorbate, FeAA; comprised of 150 µM FeSO4 and 750 µM ascorbic acid). All sperm suspensions were incubated (37°C) for 2 h. Treatment with FeAA decreased motility and viability but increased lipid peroxidation. All doses of Mn2+ increased motility and viability but decreased LPO; however, 60 µM Mn2+ was most effective. For sperm motility, viability, and LPO level, there were significant main effects of bull, treatment, and interval, as well as their interactions. In conclusion, Mn2+ reduced the oxidative stress (LPO) caused by FeAA and improved sperm motility and viability under in vitro conditions as well as under induced oxidative stress.