An L-amino acid oxidase (TM-LAO) from the venom of Hunan Trimeresurus mucrosquamatus was purified to homogeneity by three steps including DEAE Sephadex A-50 ion-exchange chromatography, Sephadex G-75 gel filtration and Resource Q ion-exchange chromatography. TM-LAO is composed of two identical subunits with a molecular weight of 55 kD by SDS-polyacrylamide gel electrophoresis. The molecular weight was different with that of LAO purified from the same species distributed in Taiwan that was 70 kD. The 24 N-terminal amino acid sequence of TM-LAO is ADNKNPLEECFRETNYEEFLEIAR, which shares high similarity with other Viperid snake venom LAOs and has moderate similarity with Elapid snake venom LAOs. Further studies found that TM-LAO inhibited the growth of E. coli, S. aurues and B. dysenteriae. TM-LAO also showed cytotoxicity and platelet aggregation activity. All the biological activities were eliminated by catalase, a H(2)O(2) scavenger. It was shown that these biological effects were possibly due to the formation of H(2)O(2) produced by TM-LAO.