Shrimp head is susceptible to autolysis under certain conditions,the protein in it is degraded into soluble protein,peptides and amino acids,and some peptides are active peptides which can inhibit the ACE enzyme activity.At present,many ACE inhibitory peptides derived from food protein have been developed.In the present study,two ACE inhibitory peptides(Tyr-Pro and Leu-Pro/Ile-Pro)were highly purified from the shrimp head(Litopenaeus vannamei)autolysate by extra fine membrane and a series of column chromatographies.In the first autolysis solution of shrimp head was consecutively extracted through extra fine membrane with molecular weight cut-offs(MWCO)at 8,5,3 ku,respectively.The active results shown that filtrate through MWCO at 3 000 u had the highest ACE inhibitory activity.The crude filtrate through MWCO at 3 ku was purified by Sephadex G-25 gel chromatography,SP Sephadex C-25 anion exchange chromatography as well as Sephadex G-15 gel chromatography,respectively.After that,the ACE inhibitory activity of purified filtrate almost increased by 8 times(IC₅₀=0.19 mg/mL)that of crude filtrate.The high active collected fraction from Sephadex G-15 gel chromatography was carried out by RP-HPLC(High-Performance Liquid Chromatography)twice for the further purification and two kinds of dipeptide were obtained,and the identification of dipeptide by mass spectra showed that they were Tyr-Pro and Leu-Pro/Ile-Pro,and the molecular weight was 279 u and 229 u,respectively.