Abstract: Objective To study the effects of pseudolaric acid B (PLAB) combined with 9-cis retinoic acid (9-cis RA) on the growth inhibition of human leukemia cells. Methods Human leukemia cells of the line HL-60 were cultured and then divided into 4 groups: control group; 9-cis RA group(9-cis RA, a RXRα ligand, was added); PLAB group (PLAB, a PPARγ ligand, was added) and combination group（9-cis RA and PLAB，were both added）. 96 h later the cell growth inhibition rate was detected by MTT assay. Flow cytometry and Hoechst33342/PI staining were used to detect the cell cycle and apoptosis. RT-PCR was used to detect the mRNA expression of RXRα and PPARγ. Results PPARγ and RXRα were expressed in HL-60 cell line. The cell proliferation was inhibited by PLAB combined with 9-cis RA in dose-dependently manner. HL-60 cells exhibited typical apoptotic morphological alteration and sub-G1 peak. PLAB combined with 9-cis RA significantly enhanced the mRNA expression of RXRα and PPARγ. Conclusion PLAB enhances the growth inhibitiory effect of 9-cis RA on human leukemia cells by the mechanism of induction of apoptosis.