This paper studies trace lipid's impact on the solubility decrease of soy protein isolate(SPI) in long-term storage.Three groups of SPI sample including SPI control,SPI with 2% non-oxidized soybean oil,and SPI with 2% oxidized soybean oil were prepared and sealed by vacuum.During 12 weeks storage,solubility,protein carbonyl content,surface free sulfhydryl group content,total sulfhydryl group content,and free amino group content were tested.It showed that the solubility of three groups decreased in a varied way: solubility of SPI with 2% non-oxidized soybean oil decreased the fast and its final solubility was the lowest in three groups.There was no significant difference in protein carbonyl content,total sulfhydryl group content,and free amino group content during storage,but surface free sulfhydryl group content of SPI(control) was constantly higher than other two groups.Results indicated that protein oxidation occurred in SPI during storage,oxidized oil speeded up the solubility decrase.However,oxidized oil was not the only factor affected protein oxidation.The main factor which caused the decrease of solubility needs to be further studied.