Abstract：The purpose of this study was to investigate the effect of 7-d oral quercetin supplementation on cycling time to exhaustion, and cycling-induced oxidative stress and inflammation in adults. Ten healthy adults were recruited to perform a randomized single blind cross-over study with 7-d quercetin (1,000 mg/day) and placebo supplementation, which was separated by a 7-d washout period. All participants performed a single bout of cycling exercise challenge at 75% maximal oxygen uptake (VO_(2max)) and time to exhaustion was recorded after completion of 7-d quercetin or placebo supplementation in a randomized order. Blood samples were taken before and after exercise challenge to assess the total antioxidant capacity (TAC), superoxide oxide dismutase (SOD), and malondialdehyde (MDA) levels. Inflammatory biomarkers, including interleukin-6 (IL-6), tumor necrosis factor-α (TNF-α), creatine kinase (CK), and myoglobin (Mb) were also determined in the blood. The results showed that time to exhaustion was significantly higher in quercetin trial compared to those in placebo. Oral quercetin supplementation significantly increased SOD activity and decreased MDA levels after 75% VO_(2max) cycling exercise challenge. Exercise-induced IL-6 elevation was significantly attenuated, and CK was also similarly responded to quercetin supplementation. However, there were no significant differences in TNF-α and Mb levels between the trials. We conclude that short-term oral quercetin supplementation enhances cycling performance of adults, which may be due the increased antioxidant capacity and attenuated exercise-induced oxidative stress, pro-inflammatory response and muscle damage. (Full text)