Graft-versus-host disease is a rare but a potentially fatal complication that can occur after kidney transplant. Furthermore, graft-versus-host disease after kidney transplant has been reported in only a few studies. We present a rare case of graft-versus-host disease in a patient who underwent kidney transplant. A patient who underwent hemodialysis received an en bloc kidney transplantfrom a pediatric donor, and the graft function was excellent. Mild diarrhea started on postoperative day 25. Six days after the onset of diarrhea, pancytopenia worsened and fever persisted. However, there were no test findings indicating infection or adverse medical effects. Graft-versus-host disease was diagnosed after a short tandem repeat evaluation of lymphocytes from the recipient's peripheral blood, which revealed 4.7% donor cells.The findings in this study provide insight into cases where symptoms such as fever and pancytopenia of unknown cause appear after kidney transplant, and we suggest that it is necessary to differentiate these symptoms from graft-versus-host disease.