Abstract： Objective To study the effects and mechanisms of mesenthymal stem cells (MSCs)derived bone marrow of patients with chronic myelogenous leukemia (CML) on function of monocytederived dendritic cells in vitro. Methods Bone marrow mononuclear cells from CML patients were obtained and cultured. Peripheral blood mononuclear cells (PBMCs) derived from normal volunteers were isolated and cultured in DC differentiational condition. Moreover, PBMCs were co-cultured with CML bone marrow-derived MSCs (CML-MSC) or normal volunteers' bone marrow-derived MSC (normal-MSC) in DC differentiational condition. Immunophenotype and the endocytosis of monocytederived DCs were investigated by FACS. The level of IL-12 was evaluated by enzyme linked immunosorbant assay (ELISA). The immunoregulatory ability was detected by mixed lymphocyte culture assay. Results CML-MSCs or normal-MSC inhibited the up-regulation of CD1a,CD40,CD80,CD86,and HLA-DR during DC differentiation and reduced CD40,CD86,and CD83 expression during DC maturation. CML-MSCs inhibited the endocytosis of DCs and decreased their capacity to secret IL-12. CML-MSC could significantly suppress the function of DCs stimulating proliferation of T lymphocytes. Conclusion CML-derived MSCs harbored effect on the differentiation and maturation of DCs in vitro ; CML-MSC could inhibit the immunregulation of DCs.