The effects of Tabebuia avellanedae (Taheebo) on exercise endurance capacity were investigated using mice in an adjustable-current water pool. Compared to the control group, a 1.8~2.0 fold increase in swimming time was observed in mice administered hot water extract (TAW) and 80% ethanol extract (TAE) of inner bark from T. avellanedae. Blood lactate level, an important fatigue relevance factor, was significantly lower in the TAW and TAE groups than in the control group. The total phenolic contents of TAW and TAE were $93.3{pm}1.6$ and $115.7{pm}1.5mgGAE/g$, respectively. The levels of flavonoids in the extracts were $77.3{pm}1.3$ and $95.9{pm}1.7mgCE/g$, respectively. Higher antioxidant activities of TAE were observed in each assay at the same concentration as compared to TAW. Correlation between antioxidant activities of TAE with total polyphenol contents was observed. These results suggest that extracts of Taheebo increase exercise endurance capacity by elevating antioxidative potentials.