Abstract: Objective To observe the effect of ammonium molybdate on inhibiting cell proliferation and inducing cell apoptosis of human hepatoma and colon cancer. Methods After human hepatoma cell line HepG2 and colon cancer cell line HCT-116 were treated respectively with 0.101, 0.202 and 0.404 mmol·L-1 of ammonium molybdate for 24, 48 and 72 h, the morphological change was observed by optical microscope, the proliferation inhibition were detected by CCK-8 method, and the change of cell cycle was detected by flow cytometry. Results With the increased concentration and action time of ammonium molybdate, its effect on inhibiting proliferation and inducing apoptosis of HepG2 cells and HCT-116 cells was significantly enhanced, in a significant dose- and time-dependent manner. And HepG2 proliferation was inhibited more obviously than HCT-116 at low concentration of 0.101 mmol·L-1, while it was opposite at high concentration of 0.404 mmol·L-1, with statistical significance(P<0.05). Ammonium molybdate prevented not only the migration of HCT-116 cells from G1/G0 to S period, but also from G2/M to G1/G0 period. Cell cycle of HCT-116 was retarded in G1/G0 and G2/M periods and that of HepG2 was retarded in G1/G0 period. Ammonium molybdate could induce the apoptosis of HepG2 and HCT-116 cells, and the rates of apoptotic and necrotic cells were increased gradually with the increased concentration of ammonium molybdate and prolonged action time. Conclusion Ammonium molybdate has antitumor activity and could inhibit the proliferation, induce the apoptosis and change the cell cycle of colon cancer and hepatoma cells. And the effect of ammonium molybdate at high concentration on colon cancer cells is greater than that on hepatoma cells.