We investigated the effects of granulocyte colony-stimulating factor (G-CSF) on monocytic (M), promyelocytic (P)and granulocytic (G) myeloid-derived suppressor cells (MDSCs) both in bone marrow and peripheral blood of 20 healthy donors and the association of MDSCs subgroups with acute and chronic graft-versus-host disease (aGvHD/cGvHD) in 62 patients who underwent haplo-identical allogeneic hematopoietic stem cell transplantation(allo-HSCT). Patients who received a higher absolute counts of M-MDSCs or P-MDSCs exhibited lower incidence of grade II-IV aGvHD (p=0.001; p=0.031) and extensive cGvHD (p=0.011; p=0.021). In the multivariate analysis, absolute counts of MDSCs in allografts emerged as independent factors that reduced the occurrence of grade II-IV aGvHD (M-MDSCs: HR=0.087, 95% CI=0.020-0.381, p=0.001; P-MDSCs: HR=0.357, 95% CI=0.139-0.922, p=0.033) and extensive cGvHD (M-MDSCs: HR=0.196, 95% CI=0.043-0.894, p=0.035; P-MDSCs: HR=0.257, 95% CI=0.070-0.942, p=0.04). Delayed M-MDSC reconstitution was associated with aGvHD onset. The 3-year cumulative incidence of transplant related mortality and relapse, 3-year probability of disease free survival and overall survival did not differ significantly between these subgroups. Our results suggested that G-CSF-induced immune tolerance may be mediated by M/P-MDSCs in allo-HSCT.