The purpose of the present study was designed to investigate the protective effects of icariin on swimming exercise-induced oxidant stress in liver of mice. The mice were randomly divided into 4 groups (1 control group and 3 icariin treated groups). The control group received only distilled water ig, and the icariin treated groups received different doses of icariin (5, 10, and 20 mg/kg, ig) for 28 days. After 28 days, the mice performed an exhaustive swimming exercise and the levels of malondialdehyde (MDA), the activities of superoxide dismutase (SOD), glutathione peroxidase (GPx), catalase (CAT), and glutathione reductase (GR) in liver of the mice were measured. These result demonstrated that icariin supplementation could elevate the exercise endurance and possess protective effect on exercise-induced oxidant stress. Icariin supplementation elevates the SOD, GPx, CAT, and GR activities, which are accompanied by corresponding decreases in MDA levels.