It is suggested that HA-1 mismatching between hematopoietic stem cell transplanted recipients-donors is associated with acute graft-versus-host disease (aGVHD). So the aim of this study was to evaluate HA-1 frequency and examine the correlation between HA-1 disparity and GVHD patients who received transplantation from a HLA-identical sibling. DNA was extracted from 30 pairs of HLA-A2-positive Iranian recipients-donors with GVHD I-IV and 25 pairs without GVHD. All the patients received HSCT from HLA-identical siblings. HA-1 was detected by SSAbstract# P-PCR method By using SSP Minor Histocompatibility Antigen primer sets. Results: The frequency of HA-1R and HA-1H alleles in patients were 0.55 and 0.45 respectively, which showed no significance difference with these alleles frequency in donors (0.53 and 0.47, p>0.05). HA-1 disparity was detected in 8 of the 55 donor/recipient pairs (14.5%). aGVHD (grades I-IV) was occurred in 6 (75%) out of 8 patients but in spite of the higher incidence of aGVHD in the group of patients with HA-1 incompatibility, did not show any statistically significant. In conclusion, in spite of higher frequency of HA-1 disparity in GVHD+ group our data did not reflect significant association between HA-1 disparity and risk of acute GVHD.