To investigate effects of rat bone marrow mesenchymal stem cells (rBMMSC) on hematopoiesis after allo-hematopoietic stem cell transplantation (HSCT), allogeneic BMT model from Fischer 344 rats (RT-1Al) to Wistar rats (RT-1Au) was established; effects of MSCs on hematopoietic reconstitution were studied by survival rate, peripheral blood counts, histological analysis and FACS at day 30 after transplantation. The results showed that (1) MSCs from donor Fisher344 could survive in recipient irradiated by lethal dose and could be found in the thymus, spleen and bone marrow of the recipient at 30 days after cotransplantation with BM by measuring EGFP gene. (2) Cotransplanation of MSCs and BM improved hematopoietic reconstitution. Lymphocyte and platelet counts of peripheral blood in cotransplantation group were higher than those in the control group. Active hematopoiesis and increase of bone marrow nucleated cells were observed in cotransplantation group. MSCs significantly enhanced hematopoiesis of B lymphocyte and megakaryocytopoietic lineages by FACS analysis. It is concluded that (1) MSCs of Fisher344 can be found in the thymus, spleen, bone marrow of the recipients at 30 days after cotransplantion by measuring EGFP gene. (2) hematopoietic reconstitution is significantly enhanced by MSCs cotransplanted with BM.