Soy protein extract was enzymatically hydrolyzed with Pepsin.With the increase of soy protein hydrolysis,the degree of hydrolysis values varied from 0% to 7.90% after 360 min of incubation.The molecular weight distribution of soy protein hydrolysates prepared with Pepsin was determined by SE-HPLC and SDS-PAGE.The results showed that soy glycinin(11S) was selectively hydrolyzed by Pepsin.The molecular weight distribution of the hydrolysates obtained after 6 h of incubation were as follows:21.34 % were above 10 ku and 68.30 % were below 5 kDa.Soy conglycinin played a big role on the MW above 10 kDa.With the hydrolysis,free sulfhydryl content first increased and then decreased,while the content of disulfide bonds had no obvious change.The results herein were helpful for understanding the mechanism of soy protein hydrolysis with Pepsin,and could serve as a guide for the development of soy protein hydrolysate products.