Effects of α -chymotrypsin modification on degree of hydrolysis (DH), solubility, emulsifying capacity and thermal aggregation of laboratory-purified soy protein isolate (SPI) using a lipoxygenase-defected soybean (Jinpum-kong) and commercial soy protein isolate (Supro 500E) were compared. SPIs were hydrolyzed by α -chymotrypsin at pH 7.8 and 37~circC for 30 min. DHs of Supro 500E and Jinpum-kong SPI were increased by α -chymotrypsin modification, and DH of Supro 500E was higher than that of Jinpum-kong SPI. DH of α -chymotrypsin treated Jinpum-kong SPI was similar with untreated Supro 500E and DH of treated Supro 500E was the highest. Solubility, emulsifying capacity and thermal aggregation of SPIs were increased by α -chymotrypsin modification, and these changes were highly related to changes in DH. Functional properties of Supro 500E were higher than Jinpum-kong SPI in both of untreated and α -chymotrypsin treated SPIs.