Angiotensin I -converting enzyme (ACE) inhibitory peptide from silkworm pupa (Bombyx mori) was purified, modified, as well as inhibition mechanism by using molecular docking analysis. Silkworm pupa protein was hydrolyzed by neutral protease and the obtained hydrolysate was subjected to various types of chromatography to acquire peptide isolate. Then the molecular mass and amino acid sequence of the peptide was determined by MALDI-TOF/TOF MS. Subsequently, thermal and digestive stability of the peptide were explored through a high temperature processing and a simulated gastrointestinal digestion. Finally, the peptide was modified to smaller peptides and investigated their potentiate activities. Results showed that the peptide from silkworm pupa was determined to be Gly-Asn-Pro-Trp-Met (603.7 Da) with IC50 21.70 mu M. Stability testing showed that ACE inhibitory activities were not significantly changed at temperature from 40 to 80 degrees C as well as during in vitro gastrointestinal digestion. The inhibitory activity of four modified peptides were Trp-Trp > Gly-Asn-Pro-Trp-Trp >Asn-Pro-Trp-Trp > Pro-Trp-Trp, and the IC50 of Trp-Trp was 10.76 mu M Docking simulation revealed that the inhibitory activity was closely related to the spatial structure of peptide and zinc ions. The purified peptide and four modified peptides may be beneficial as functional food or drug for treating hypertension. (C) 2016 Elsevier Ltd. All rights reserved.