A 59-year-old woman with end-stage renal disease of diabetic nephropathy who had been on maintenance hemodialisis for 4 years, underwent a living-unrelated renal transplantation 6 years ago. She was admitted to our hospital, because of a low grade fever and edema. Ultrasonography revealed the cyst with heterogeneity structure in the upper pole of the transplanted kidney. Magnetic resonance imaging showed a high-intensity cystic mass measuring 68×53 mm. As fever and laboratory data did not improve sufficiently by the treatment with antibiotics, echo-guided puncture and drainage were performed for the abnormal structure in the upper pole of the transplanted kidney. In the culture of the purulent aspirate drained from renal cyst, Escherichia coli was isolated. To our knowledge, this is the first report of infected renal cyst of the graft in a renal transplant recipient in the world.