The objective of this study was to determine the effects of oral coenzyme Q10 (CoQ10) supplementation on performance during repeated bouts of supramaximal exercise. This randomized, double-blind, crossover study was composed of two 8-week periods of supplementation with either 100 mg.d(-1) CoQ10 or placebo. Fifteen healthy and sedentary men participated in the study. Five Wingate tests (WTs) with 75 g.kg(-1) body weight load with 2-minute intervals between tests were performed 3 times at baseline, after CoQ10, or placebo supplementation during the study period. Peak power (PP), mean power (MP), and fatigue index were calculated. During the 5 WTs, PP and MP tended to decrease and fatigue index tended to increase in all groups (p < 0.05). Peak power decreased with CoQ10 and placebo supplementation during the WT1, WT2, and WT2 (p < 0.05). Mean power increased only with CoQ10 supplementation during the WT5. Fatigue indexes decreased with CoQ10 supplementation, but these decreases did not differ from that seen with placebo supplementation. According to these results, CoQ10 may show performance-enhancing effects during the repeated bouts of supramaximal exercises and CoQ10 might be used as ergogenic aid.