A phospholipase A2 (DE-I) was purified from Trimeresurus okinavensis (Hime-habu) venom by gel filtration on Sephadex G-50 followed by ion-exchange chromatography on DEAE-cellulose. It comprises 123 amino acid residues including 14 half-cystine residues. The primary structure of the enzyme has been elucidated. The sequence and invariant amino acid residues of DE-I resemble those of phospholipases A2 from venoms of Viperidae and Crotalidae (Group II) snake venoms. The phospholipase A2 from T. okinavensis contains two histidine residues which are located at the N-terminal residue and at the active centre (histidine-47). The acidic phospholipase A2 (DE-I) is not toxic.