Abstract: Myelodysplastic syndrome (MDS) comprise a group of clonal hematological malignancies characterized by bone marrow (BM) ineffective hematopoiesis and increased risk for progression to acute myeloid leukemia. The altered BM mesenchymal stem cells (MSC) play a pivotal role in the evolution and propagation of MDS. Compared to normal MSC, MSC in MDS often exhibit altered Cytogenetic, epigenetic, differentiation and functional properties , moreover, high MSC density is associated with poor risk independent of known prognostic factors, which translated into a significantly diminished ability to support normal hematopoiesis, facilitates survival of malignant hematopoietic cells, ultimately promote disease progression and transform to acute myeloid leukemia.Therefore, Characterization of key steps in the pathogenesis of MDS will lead to new approaches to treat patients with this disease.