Our previous studies demonstrated that genistein and daidzein were able to change several membrane characteristics of human colon tumor (HCT) cells. As the condition of the membrane plays important roles in tumor progression, evidence led to the hypothesis that genistein and daidzein had an inhibitive effect on the metastasis of malignant cells. To validate this hypothesis, we employed a highly metastatic melanoma cell line (murine K1735M2) to study the effects of genistein and daidzein on the metastatic events of K1735M2. Studies show that genistein (30 -μmol/L) and daidzein (30 -μmol/L) have an obvious inhibitive effect on the proliferation of K1735M2. In addition, genistein and daidzein markedly inhibit the invasion of K1735M2 cells into a collagen I gel matrix and also inhibit migration through a polycarbonate filter. The inhibitive effect of genistein on migration is dose-dependent. These results support the hypothesis and imply that genistein and daidzein might be potential chemopreventive agents for melanoma treatment.