Abstract: AIMTo study the antioxidant activity of 2-ethyl-3-hydroxy-6-phenylthio-4(1H)-pyridone (HPP). METHODSThe scavenging effect of HPP on hydroxyl radical was determined using electron spin resonance (ESR), DMPO was used as free radical capture and the fluidity of the mitochondria membrane of mouse liver was measured using fluorescence spectrophotometer, DPH was used as fluorescence probe. The mice were injected ip with HPP 0.1, 0.4 and 1.6 mg·kg^-1 once daily for two weeks. The serum and the liver mitochondria of the tested mice were separated to quantify the liver GSH-Px and the serum SOD activities through colorimetric reaction. MDA was assayed by TBA color reaction. RESULTSIt is evident that HPP considerably scavenged hydroxyl radical and significantly increased the fluidity of the mouse liver mitochondria membrane. HPP greatly enhanced the serum SOD activity and the liver mitochondria GSH-Px activity while the MDA levels in mouse liver tissues decreased. CONCLUSIONThe antioxidant activity of HPP is evident.