Abstract Previous studies demonstrated Ganoderma lucidum polysaccharides (GL-PS), a form of bioactive β-glucan can stimulate the maturation of monocyte-derived DCs (Mo-DCs). However, the question of how leukemic cells especially in monocytic lineage respond to GL-PS stimuli remains unclear. We hypothesized that GL-PS may also have an effect on leukemic monocytic cells In this study, we used human dendritic cell (DCs) in vitro culture model with leukemic monocytic cell-lines THP-1 and U937 as cell sources. We treated the cells with purified GL-PS (100 μg/mL) or GL-PS with GM-CSF/IL-4 (cocktail). GL-PS alone induced proliferative response on both cell-lines with more markedly on U937. But it induced THP-1 cells to differentiate into cells with typical DC morphology. Additive maturation effect can be shown when THP-1 cells were stimulated with the cocktails shown by significant increase in HLA-DR, CD40, CD80 and CD86 which express in normal peripheral blood Mo-DCs. The GL-PS THP-1 DCs had similar antigen-uptake ability as the Mo-DCs positive control. However, we found that GL-PS THP-1 DCs could not induce allogeneic T cell proliferation in the one-way mixed lymphocyte reaction as Mo-DCs or THP-1, suggesting GL-PS THP-1 DCs were immunotolerogenic in nature. Our data indicated that the GL could induce monocytic leukemic cell proliferations as well as differentiate particular leukemic cells to DCs with immunosuppressive action. The possible clinical impact has to be carefully investigated.