The cytotoxicity of animal venoms (snakes, insects and marine animals) was measured against SNU-1 (stomach cancer cells) by dye uptake assay (MTT method). And also L-amino acid oxidase (AAO) activity of the venoms was compared. Among them, the venom from Ophiophagus hannah (king cobra) showed a strong AAO activity as well as a high potent cytotoxicity. Cytotoxic protein having a AAO was then partially purified by HPLC-GPC and two fractions (Fr. I and Fr. II) were collected. The $IC_{50}$ values of Fr. I and Fr. II were 0.19 ${mu}g/ml$ and 1.36 ${mu}g/ml$, respectively. The results suggested that the cytotoxicity of king cobra venom may be due to its AAO activity.