Abstract: Human promyelocytic leukemia cells (HL-60) was used to study the effect of sodiumselenite on phosphorylation of retinoblastoma (RB) protein and its anticancer mecha-nism.Method of western--blotting and flow cytometric analysis were undertaken.Theresult of western-blotting showed that 4 days after treatment of 5.8μmol/L.Na2SeO3,the amounts of the phosphorylated RB protein decreased some 49%that of controlgroup,while the hypophosphorylated RB protein increased a little.However, in this selenium group the phosphorylated RB protein was 71.1% in total RB protein amounts.In the same time, the result of cell cycle revealed that sodium selenite could slightly arrest HL-60 cells at G2+M and S phase.The experiments studied the mechanism of sodium selenite inhibited HL-60 cells proliferation at protein molecules level.