In order to verify the bioavailability of ACE (Angiotensin Converting Enzyme) inhibitory activities ofsoybean peptides,3 kinds of soybean peptides with different hydrolysis degrees were prepared by using Alcalaseprotease to catalyze the hydrolysis of soybean protein,and the effects of simulated in- vitro digestion on the struc-ture,properties and ACE inhibitory activities of soybean protein isolates (SPI) and soybean peptides were ana-lyzed.The results show that (1) the relative molecular mass of the three kinds of soybean peptides are all less than16000,and the content of TCA soluble protein increases with the degree of hydrolysis; (2) after the simulated in-vitro digestion,SPI degrades,with its molecular size and properties tending to those of soybean peptides,and,atthe same time,soybean peptides further degrade; and (3) there is no significant difference between SPI and soy-bean peptides because the simulated in- vitro digestion results in a significant decrease of ACE inhibitory activities ofsoybean peptides and a remarkable increase of those of SPI.It is thus concluded that SPI is able to release antihy-pertensive peptides under the action of Alacalase protease,but the ACE inhibitory activities of soybean peptidesmay reduce after the simulated in- vitro digestion; and that SPI by oral administration may have the same effect oflowering blood pressure.