A 30-year-old male presented with pitting edema. He had received a kidney transplantation 3 months previously. His serum creatinine level was increased, and a renal ultrasound showed hypoechoic fluid collection in the perirenal space and pelvic cavity. We conducted sono-guided percutaneous drainage of the fluid collected in the pelvic cavity. The chemistry of the peritoneal fluid was more equivalent to serum chemistry values than to urinary values. Simple aspiration and treatment with antibiotics were performed. We have presented a case of lymphocele after kidney transplantation. This case suggests that physicians should remember how to differentiate the pelvic cavity fluid collection in patients who have received a kidney transplant.