Abstract: AIM: To study the effects of polysaccharides isolated from mycelium of Ganoderma lucidum(MGLP1 and MGLP2) on HL-60 cell apoptosis. METHODS: The in vitro effect of MGLP1 and MGLP2 on the proliferation of HL-60 cells were evaluated by MTT assay. DNA gel electrophoresis and flow-cytometric analysis were used to determine the apoptotic cells. RESULTS: MGLP1 did not show inhibition of HL-60 cell proliferation in vitro. When the concentrations of MGLP2 were at higher doses (187.5～750 μg.ml^-1), it slightly inhibited HL-60 proliferation. Furthermore, MGLP1 and MGLP2 showed no effect on inducing HL-60 apoptosis even at a high dose of 600 μg.ml^-1. However, the conditioned medium from MGLP1 and MGLP2 activated splenocytes (MGLP1-S-CM, MGLP2-S-CM) markedly induced HL-60 apoptosis. DNA gel electrophoresis showed obvious DNA “ladder”. Flow-cytometric analysis revealed that few 8.0%±0.4% apoptotic cells were seen in the control cultures, while MGLP1-S-CM and MGLP2-S-CM treatment resulted in significant increase in the apoptotic population in the HL-60 28.1%±0.3%, MGLP1-S-CM; 32.4%±0.9%, MGLP2-S-CM). CONCLUSION: MGLP1 and MGLP2 showed no obvious effect on HL-60 cell proliferation and inducing HL-60 apoptosis in vitro, whereas MGLP1-S-CM and MGLP2-S-CM markedly induced HL-60 apoptosis.