Silkworm pupa (Bombyx mori) protein (SPP) was treated by ultrasound, and then was hydrolyzed using alcalase. The hydrolysate with the highest ACE inhibitory activity was obtained at hydrolysis of 50 min when SPP was treated at power of 410W/100 ml for 32 min. The hydrolysate was fractionated by ultrafiltration, and peptide with the highest ACE inhibitory activity was purified from <5 kDa fraction using gel filtration and RP-HPLC. A novel peptide was identified as Lys-His-Val (IC50 = 12.82 mu M), and it was stable against the gastrointestinal proteases. The molecular docking study revealed that ACE inhibitory activity of the tripeptide was mainly attributed to the hydrogen bond interactions and Zn(II) interaction between the tripeptide and ACE. These results suggest that the tripeptide is a potential natural ACE inhibitor that can be used as drug or functional food ingredient. (C) 2015 Elsevier Ltd. All rights reserved.