1- Objectives, Investigation on adult human mesenchymal stem cell transplantation on treatment of steroid-refractory acute graft-versus-host disease 2-Design, the study is designed as a phase 1-2, parallel, open-label, single-centric randomized clinical trial. In the beginning, among patients with acute graft-versus-host disease who eligible for inclusion criteria for cell therapy, ten patients as recipients and ten patients as control will be selected. 3- Setting and conduct, All stages of the project explain for each patients as recipient and healthy volunteers as donor, then if they want to enter the project inform consent would be obtained. Then, mesenchymal stem cells (MSCs) obtained via donors bone marrow aspiration would be cultured. After propagation of the cells, each patient will receive MSCs intravenously. Patients will be examined and visited by medical team on 1st, 4th, 7th, 14th, 21th, 28th days and six months after cell therapy and clinical and para-clinical indexes of patients will be assessed. 4- Participants including major eligibility criteria, steroid-refractory acute graft-versus-host disease with grade II to IV. 5- Intervention, Each patient will receive 1 million MSCs /kg by IV injection. 6- Main outcome measures (variables), Include assessing the efficacy of treatment by graft-versus-host disease clinical grading, acute and late onset side effects of mesenchymal stem cell therapy.