We report a diabetic renal transplant recipient with cytomegalovirus (CMV) disease who presented with tarry stool diarrhea because of multiple colonic ulcerations. Histopathology revealed diffuse colonic ulcers following a process of ischemic vasculitis. The colonic ulcers disappeared dramatically after 2 wk of intravenous ganciclovir therapy. Hyper-immunosuppression was initially suspected but acute rejection (AR) developed after immunosuppressive reduction during the ganciclovir therapy. The AR was successfully reversed and the dosage of cyclosporine was returned to the same level prior to the onset of CMV disease. Our experience suggests that ganciclovir is quite effective for healing colonic ulcers caused by CMV and acute allograft rejection may occur during therapy.