Abstract: This study mainly investigated the changes of physical- chemistry and emulsifying properties induced by hydroxyl radical- stressed soybean protein isolate ( SPI) .SPI was exposed to a hydroxyl radical- generating system ( HRGS) under different H2O2concentrations ( 0.1¹5mmol / L) for 1h.The results revealed that the carbonyl content of SPI was significantly increased ( p < 0.05) and the free amino content obviously increased after the first down ( p < 0.05) . When the H2O2 concentration was 5mmol / L, the SPI exhibited the higher emulsifying activity and emulsion stability, as well as the lowest turbidity and highest ζ- potential ( p < 0.05) .In addition, under the excessive oxidation conditions, the particle size of SPI was significantly reduced ( p < 0.05) .The results showed that oxidation could be changed the physicochemical and emulsifying properties of SPI and moderate oxidation could improve the emulsifying properties of SPI.