Objective:To study the anti-tumor activity of ginkgo albumin (GA) and its mechanism. Method: Molecular weight of GAⅡa was detected by MS (mass spectrum). The antioxidative effect of GA was studied by deoxyribonucleic acid method and nitroblue tetrazolium (NBT) photo-reduction, and the anti-tumor activity of GA on S180 sarcoma was studied both in vivo and in vitro. Results: Molecular weight of GAⅡa was 29 248u. GA had strong scavenging effect on superoxide radical and hydroxyl radical. The growth of S180 both in vitro and in vivo was inhibited significantly by GA. Conclusion: The anti-tumor activity of GA was probably related with its antioxidative effect.