The combined effects of water-soluble fraction of Moschus (ME) and anti-tumor drug mitomycin C on the proliferation of human tumor cell-lines were estimated by MTT colorimetric assay. ME inhibited the proliferation of Hep G2, A540, HeLa, KHOS-NP and Balb/c 3T3 cells. Also, ME increased the cytotoxicity of mitomycin C on Hep G2, A549 and HeLa cells. In addition, ME enhanced the cell viability of murine splenocytes and human lymphocytes at the concentration of 100㎍/㎖. These results indicate that ME inhibits the proliferation of human tumor cells and increases the cytotoxicity of mitomycin C without cytoxicity on immune cells.