Abstract： Objective To investigate the impact of auto and allogenic mesenchymal stem cells (MSC) transplantation on hematopoietic reconstitution. Methods MSC from auto, donor bone marrow or embryonic tissue were cultured and expanded in vitro in the serum culture system. Five patients received hematopoietic stem cell transplantation (HSCT) were investigated. Case 1 of systemic lupus erythematosus and Case 2 of non-hodgkin' s lymphoma (NHL) received auto MSC transplant before auto-HSCT. Case 3 of paroxysmal nocturnal hemoglobinuria received HLA-identical allogenic MSC transplant before HLA-identical allo-HSCT.Case 4 of chronic myelocytic leukemia and Case 5 of NHL had delayed hematopoietic reconstitution (129th and 78th day, respectively) after allo- and auto-HSCT, respectively, and received MSC from embryonic tissue.Results Case 1, 2 and 3 had no manifested side effects after MSC transplantation combined with HSCT.Neutrophil count of case 1, 2, and 3 were over 0.5 ×109/L at 1st, 10th and 10th day, respectively, platelet count were over 20 ×109/L at 1st, 8th and 33th day, respectively, and agranulocytosis at Ost, 7th and 12th day, respectively. The treatment of embryonic tissue MSC transplant was confirmed to fail for Case 4 and 5.Conclusion The time of MSC transplant has a great impact on hematopoietic reconstitution. MSC transplantation and HSCT performed simultaneously can improve hematopoietic reconstitution. However, the impact of MSC on patients with delayed hematopoietic reconstitution after HSCT needs further study.