An antioxidative compound with effective exercise-enhancing potential was isolated from the ethanolic extract of Pseudosasa japonica leaves. The ethanolic extract was partitioned in the order of hexane, chloroform, ethyl acetate, and water. Of the 4 fractions, the ethyl acetate-fraction (PJE-E) showed profound scavenging activity on superoxide anion- and ABTs cation radicals. Thin layer chromatography (TLC) and high performance liquid chromatography (HPLC) were conducted to isolate a compound with antioxidative activity on exercise endurance capacity from the PJE-E. The structure of the resulting compound was identified as ferulic acid by $^1H/^{13}C$ nuclear magnetic resonance (NMR). This ferulic acid was orally administered to mice for 18 days and its effect on exercise endurance capacity was investigated using an adjustable-current water pool. Compared to the control group, a 1.8 fold increase in swimming time was observed in the ferulic acid-administered mice. Results indicate that ferulic acid from P. japonica leaves might contribute to the potent exercise-enhancing effect.