This study was aimed to investigate the effect of all-trans retinoic acid (ATRA) combined with SBA-Na on the biologic activities of human leukemia K562 and Kasumi-1 cell lines and their mechanism. The ATRA solution of 10(-6) mol/L (W1), 10(-4) mol/L (W2) and the SBA-Na solution of 100 µg/ ml (Z1) and 200 µg/ml (Z2) were prepared respectively. The K562 and Kasumi-1 cells were treated with W1, W2, Z1, Z2, W1 + Z1 and W2 + Z2 respectively, at same time, the blank control was set up. The cell morphology and growth in different treated groups were observed under light microscope. The CCK-8 method was used to detect the proliferation ability of cells, the cell growth curves were drawn, the inhibitory rate of cells was calculated. The flow cytometry with PI single staining and PI/Annexin V double stainings was used to detect the change of cell cycle and apoptosis of 2 cell lines treated with different drugs. The RQ-PCR was used to detect the change of Cyclin A mRNA expression in K562 cells. The results showed both ATRA and SBA-Na displayed inhibitory effect on cell proliferation, and the combination of these two drugs had stronger effect. As compared with the control group, the cell cycle distribution were changed obviously, and the apoptosis increased more significantly in treated groups, especially in group of ATRA combined with SBA-Na. The Cyclin A mRNA expression was up-regulated in Z1 group, while Cyclin A mRNA expression was down-regulated in other groups. It is concluded that both ATRA and SBA-Na can inhibit the proliferation of K562 and Kasumi-1 cell lines and promote their apoptosis. This effect may be stronger when both drugs combined. For K562 cells, the inhibitory effect may be accomplished through down-regulation of Cyclin A mRNA.