A 10-year-old female Pomeranian weighing 2.25 kg with a history of gradual weight loss and an intraabdominal mass confirmed with ultrasonography at a local hospital was referred to the Veterinary Medical Teaching Hospital, Jeju National University. Physical examination revealed abdominal distention. Blood analysis revealed hypoglycemia (57 mg/dL; reference range, 60-110 mg/dL). On abdominal ultrasonography, a heterogeneously hyperechoic mass measuring 7.51 × 10.6 cm was found at the level of the left kidney. Computed tomographic findings showed a unilateral left kidney mass with a 10-cm diameter and vessel contrast enhancement in the corticomedullary phase. Unilateral nephrectomy and ovariohysterectomy were performed because left ovary enlargement was observed during surgery. The renal mass was adjacent to the aorta and vena cava and attached to a portion of the small intestine, greater omentum, and left ovary. The mass was huge (12.5 × 10 × 7 cm) and was 16.5% of the body weight. Histopathological examination revealed renal cell carcinoma (RCC) and ovarian metastasis. After surgery, clinical signs improved remarkably, and serum glucose level returned to normal. As RCC is resistant to radiation and chemotherapy, the owner decided not to proceed with postoperative adjunctive therapies. To the best of our knowledge, this is the first case report of ovarian metastasis with huge RCC in a dog.