Objective To study the influence of IL-33 on the Hematopoietic stem cells and progenitor cells . Methods Cells from the peripheral blood , spleen, thymus and bone marrow were stained with indicated antibodies and analyzed by flow cytometry . The LT-HSCs were sorted and culture using in vitro clonogenic assay . Results The percentage of B cells and T cells was decreased and the percentage of M cells was increased in the peripheral blood from IL -33 transgenic mice .Compared with the wildtype mice , the number of HSCs , MPPs and CLP was decreased;meanwhile the number of CMP and GMP was increased in the bone marrow from IL-33 transgenic mice .An in vitro clonogenic assay showed that LT-HSCs increased the ability to self-renew from IL-33 transgenic mice .And the percentage of S-G2-M stage hematopoietic stem cell was increased from IL-33 transgenic mice .Conclusion IL-33 increase the myeloid differentiation in hematopoietic stem cells .