Abstract: The present invention relates to an anti-tumor agent comprising Salmosin which is a novel disintegrin containing Arg-Gly-Asp(RGD) sequence and derived from venom of Korean snake, Agkistrodon halys brevicaudus, as an active ingredient. Salmosin is a disintegrin which blocks the function of &agr;v&bgr;3 integrin and strongly inhibits tumor angiogenesis, tumor metastasis as well as growth of solid tumor. Salmosin does not exhibit cytotoxicity within an effective dose range where tumor growth is efficiently suppressed without any untoward effect on preexisting blood vessels and normal angiogenesis. Accordingly, Salmosin can be applied for the development of potent anti-tumor drugs which are effective for various types of cancers.