Some of the genotypes of cytokines are associated with acute graft versus host disease after bone marrow transplantation. The purpose of the present investigation was to find out the possible association between transforming growth factor beta-1 (TGF-beta1) codon 25 polymorphism (rs:1800471) and acute graft versus host disease (aGVHD) after bone marrow transplantation from the sibling with the similar HLA among the Iranian population. In this retrospective case-control investigation, 172 subjects including 86 Iranian patients and their siblings with the similar HLA as donor/recipient pairs were recruited. All of the patients were diagnosed with one group of blood disorder consisting of Acute Myeloid Leukemia (AML)=40, Acute Lymphoblastic Leukemia (ALL)=25 and Chronic Myeloid Leukemia (CML)=21. PCR-SSP method was carried out to ascertain TGF- beta1 codon 25 G/C polymorphism genotypes. The frequency of TGF- beta1 codon 25 GG, GC and CC genotypes among all cases were 77.3%, 21.5% and 1.2%, respectively. Recipients with the GG genotype developed severe aGVHD significantly more than those with CC or GC genotypes (Odds Ratio =12.133, P=0.015). Genetic background of TGF-beta1 may be involved in aGVHD development and/or severity in the patients who received Bone Marrow Transplantation (BMT) from their siblings with the similar HLA among the Iranian population.