Enzymatic hydrolysis of soybean protein isolates and debittering of hydrolysate were studied. Neutral protesse ASI.398 was shown to be the best biocatalyst for the hydrolysis of soybean protein isolates and debittering of hydrolysate. For the hydrolysis reaction, the optimal pH value, temperature, substrate concentration, enzyme dosage and reaction time were 7.0, 50℃, 5%, 8%, and 6h, respectively. For the debittering reaction, the best activated carbon,β-cyclodextrin and citric acid were: 1%, 0.8% and 0.08%, respectively.