Agkistrodon halys venom contains various enzymes,most of which are hydrolyticenzymes except L-amino acid oxidase. Crude A. halys venom and the injectionpowder prepared from the venom were cytotoxic in vitro to various tumor cells as wellas normal proliferating cells.After purification of the-crude venom,the in vitro cyto-toxic substance was identified as L-amino acid oxidase.The in vivo antitumor effectof the venom infection powder was investigated, but no clear suppression of thegrowth of tumor cells was observed. Thrombin-like coagulant enzyme was also isolatedfrom the crude venom. Differences in the properties between this enzyme and bovinethrombin were examined. The venom coagulant enzyme showed a microheterogeneitydue to varying contents of sialic acid. Presence of several endopeptidases(proteinases)was also demonstrated in the venom which may participate in the degradation offibrin clot. Agkistrodon halys venom contains various enzymes,most of which are hydrolyticenzymes except L-amino acid oxidase. Crude A. halys venom and the injectionpowder prepared from the venom were cytotoxic in vitro to various tumor cells as wellas normal proliferating cells.After purification of the- The crude venom, the in vitro cyto-toxic substance was identified as L-amino acid oxidase.The in vivo antitumor effect of the venom infection powder was investigated, but no clear suppression of the growth of tumor cells was observed. Thrombin-like coagulant enzyme was also Isolated from the crude venom. Differences in the properties between this enzyme and bovinethrombin were examined. The venom coagulant enzyme showed a microheterogeneity to varying contents of sialic acid. Presence of several endopeptidases (proteinases) was also demonstrated in the venom which may participate in the degradation Offibrin clot.