1. The major phospholipase A2 (PLA-DE4) of the venom of Trimeresurus purpureomaculatus (shore pit viper) has been purified to electrophoretic homogeneity. 2. The isoelectric point of the purified enzyme was determined to be 4.20, and the mol. wt was 31,700 as estimated by Sephadex G-75 gel filtration chromatography; and 14,000 as estimated by SDS-polyacrylamide gel electrophoresis. The purified enzyme hydrolyzed phosphatidylcholine (PC) faster than phosphatidylethanolamine (PE), whereas phosphatidylserine (PS) was not hydrolyzed at all (PC greater than PE greater than PS =0). However, in reaction system consisted of mixtures of PC and PS, phosphatidylserine was effectively hydrolyzed by the enzyme. 4. The phospholipase A2 exhibited edema-forming activity but not hemolytic, hemorrhagic or anticoagulant activities. It was not lethal to mice at a dosage of 10 micrograms/g by i.v. route.