With hydrolysis test as an orientation,the major autoenzyme was purified from the head of white shrimp(Penaeus vannamei) by sulfate precipitation,gel filtration on Sephadex G-100 followed by ion-exchange chromatography DEAE-DE52.The autoenzyme was then identified by inhibitor tests and SDS-PAGE analysis.The results showed the major autoenzyme from the head of white shrimp had a specific activity of 2.2×106 U/g with a 96.90-fold increase over that of the crude enzyme extract.This autoenzyme was inhibited by serine protease inhibitor phenyl methyl sulfonyl fluoride(PMSF) with the inhibition rate being 91.3%,and illustrated as a single band in SDS-PAGE with the same distance as that of standard trypsin.These results indicated that trypsin was the major autoenzyme in the head of white shrimp.