The polyphenol oxidase in red-fleshed peach skin was extracted in Tris-HCl buffer and purified by ammonium sulfate precipitation and column chromatography.One pure single band was obtained using electrophoresis.According to the Michaelis-Menten constant,the optimal substrate of the PPO was pyrogallol.The optimal temperature and pH of the PPO at 420 nm was 45℃ and 7.0-7.5,respectively.PPO was more stable in neutral pH environment and below 55℃.Circular dichroism (CD) spectrum,fluorescence spectroscopy,and dynamic light scattering were used to characterize the structures of the PPO.Result of CD spectrum showed that the secondary structure of PPO contained 50.61% α-helix,32.47% β-folded,10.83% β-corner and 6.21% random coil.Result of fluorescence spectroscopy showed that the maximum emission wavelength of PPO was 352 nm.The intensity of fluorescence was 133.9,indicating that the fluorophore was in a polar hydrophilic environment.Result of dynamic light scattering showed that the particle size distribution was concentrated at 255 nm,indicating that the PPO was in a gathering state.