Background Allogeneic peripheral blood stem cell transplantation from unrelated donors (UR-PBSCT) is an altative treatment for many hematologic diseases due to lack of human leukocyte antigen (HLA)-identical sibling donors.This study aimed to evaluate the impact of the degree of the HLA match on the clinical efficacy of UR-PBSCT.Methods Patients who underwent UR-PBSCT from September 2003 to September 2012 were retrospectively investigated.They were divided into three groups according to high-resolution molecular typing.SPSS version 17.0 was used to analysis and compare the statistics of engraftment,incidence of GVHD,other complications and survival among the groups.Results One hundred and eleven patients received UR-PBSCT,60 of them with an HLA matched donor (10/10),36 of them with a one locus mismatched donor (9/10),and 15 of them with a two loci mismatched donor (8/10).Similar basic characteristics were found in the three groups.No differences were found in engraftment of myeloid cells or platelets in the three groups (P＞0.05).Two-year cumulative incidence of relapse,overall survival (OS) and disease-free survival (DFS) among those three groups were similar (P＞0.05).The cumulative incidence of 100-day Ⅲ-Ⅳ aGVHD in the HLA matched group and the one HLA locus mismatched group were significantly lower than that in the two HLA loci mismatched group (3.3％,8.6％,and 26.7％,P=0.009).The occurrence rate of new pulmonary infections in the HLA matched group was lower than in the two HLA mismatched groups (26.67％,52.78％,and 41.18％,P=0.035).The cumulative incidence of 100-day and 2-year transplantation related mortality (TRM) in two HLA loci mismatched group was higher than in the HLA matched group and in the one HLA locus mismatched group,(8.4％,11.8％ and 33.3％,P=0.016) and (12.3％,18.7％ and 47.5％,P=0.002).Conclusions HLA mismatch will not significantly impact the engraftment or 2-year survival after UR-PBSCT,but two mismatched HLA loci may increase the cumulative incidence of severe aGVHD and TRM.