Degreased silkworm pupae protein was the byproducts of filature,we have found that the hydrolysates of silkworm protein hydrolyzed by acid protease(Aspergillus usamii NO.537) with Angiotensin I-Converting Enzyme inhibitory activity,but there were many protein components in it,what the hydrolyzing characteristics of these protein were,and how about the relationships between the hydrolyzing characteristics and Angiotensin I-Converting Enzyme inhibitory activity were the purposes of this paper.