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Aim To investigate the impact of patients with anti-HLA antibodies or with donors mismatched at HLA-DP locus on outcomes after unrelated-donor hematopoietic stem cell transplantation (HSCT). Method We explored the data from 123 patients that received allo-HSCT matched for HLA-A, B, C, DRB1, DQB1, and DQA1 (12/12) from unrelated donors from the CMDP with a 2-year follow up. The examination of anti-HLA antibodies was scheduled at 3 time points: before the start of conditioning treatment and 1 month, 3 months after transplantation. Results The presence of anti-HLA antibodies detected before and 1 month, 3 months after transplantation was 37.4% (46/123), 40.2% (47/117), 22.6% (24/106), respectively. 16.4% (18/110) recipients with donors matched in HLA-DPA1 and HLA -DPB1 loci, and the mismatched rate was 83.6% (92/110). Patients with preformed anti-HLA antibodies had delayed platelet recovery. Anti-HLA antibodies detected before and after transplantation were responsible for increased occurrence of grade 2–4 acute graft-versus host disease (aGVHD) and reduced overall survival (OS), especially in acute myeloid leukemia and myelodysplastic syndrome patients. Pre-existing HLA-Ab was an independent risk factor for the GVHD and OS. Unfortunately, we found that HLA-DP mismatches have nothing to do with outcomes after transplantation. For HLA-Ab negative group, HLA-DP matched subgroup had a modest trend towards a lower rate of aGVHD, and a higher occurrence of OS and DFS compared with HLA-DP mismatched subgroup. Conclusions Our results suggest that anti-HLA antibodies detected before and after transplantation had a negative effect of outcomes, but HLA-DP loci mismatches have no significance after HLA- 12/12 matched unrelated donor of allo-HSCT. Anti-HLA antibodies should be the primary consideration in the setting of HLA 12/12-matched unrelated-donor HSCT, followed by the status of HLA-DP matching. [ABSTRACT FROM AUTHOR]