The development of primary malignant tumors is a distressing complication of organ transplant. However, the emergence of de novo renal cell carcinoma from a kidney allograft is rare. A 60-year-old man underwent living kidney transplant from a spousal donor. Six years after the transplant surgery, computed tomographic evaluation confirmed the presence of a 2.8-cm-diameter solid mass in the lower pole of the allograft. Partial allograft nephrectomy was performed, and the margin surrounding the normal parenchyma was resected. The serum level of creatinine did not decrease. Here, we report a case of renal cell carcinoma in an allograft kidney that was successfully treated with nephron-sparing surgery.