The stem cell leukemia (SCL) gene is a new oncogene related with leukemogenesis. To explore the effects of antisense oligonucleotides of SCL on leukemic cells, SCL antisense phosphorothioate oligodeoxynucleotides (AS-PS-ODN) were used to treat K562 and CEM leukemic cell lines to observe the effects on proliferation, differentiation, apoptosis and SCL mRNA expression in the cells. The results showed that incubation of K562 or CEM cells with AS-PS-ODN at different concentrations led to inhibition of cell proliferation, and the inhibitory effects varied with the incubation time. The positive rate of benzidine staining in K562 cells increased significantly after the inhibition with AS-PS-ODN, compared with S-PS-ODN treatment. The characteristics of apoptosis were observed in K562 cells treated with AS-PS-ODN, but not in CEM cells. Expression of SCL mRNA in K562 and CEM cells and SIL-SCL mRNA in CEM cells decreased after incubation of AS-PS-ODN. It is concluded that SCL AS-PS-ODN inhibits specifically the proliferation of K562 and CEM cells, also decreases the level of SCL and SIL-SCL mRNA expression. AS-PS-ODN enhances erythroid differentiation and induces premature apoptosis in K562 cells.