The primary renal tumors are rare in dogs, accounting for less than 1% of all tumors, the carcinoma is more common, occurring in adult and senile animals, irrespective of gender and race. Palpable abdominal mass associated with the weight loss, hematuria and depression are common clinical signs. A nephrectomy is considered appropriate for unilateral tumors that have not been metastasis. We report a case of unilateral primary renal cell carcinoma in a dog served in clinical veterinary Carandá in Campo Grande--MS, diagnosed by ultrasound examination and confirmed by histopathological examination. It was attended a male German Shepherd dog, 9 years old, with a history of pelvic limb lameness of left, progressive weight loss two months ago, walking bent, bulging of the left abdominal region, hyporexia, polydipsia and low urine volume. On physical examination were pale mucous, temperature 39°C, emaciation and apathy intense, mild dehydration.  Palpation abdominal was found in hard consistency mass with irregular contour, extending from the left flank before umbilical region, approximately 12cm. In the series white blood count showed leukocytosis with neutrophilia with shift to left. The biochemical values were within the normal. When ultrasound examination was observed left kidney topography of the mass in measuring approximately 11cm, and the heterogeneous and hyperechoic aspect, cavitations anechoic with approximately 2cm in diameter. In the region of the mass flow was small portion preserved kidney, suggesting neoplasm in left kidney. There was no visible masses in sonographic examination in other organs. It was suggested left nephrectomy. The animal came to death eight hours after surgery. The histopathology of the surgical specimen revealed proliferation of tumor composed of round and oval cells arranged in irregular lobules and cords brought solid with little stroma, low mitotic index. The conclusion of histopathology was renal cell carcinoma. The ultrasound was instrumental in the location of the mass and orientation to conduct therapy, since the decision to nephrectomy is considered appropriate only for tumors that have not been unilateral metastasis evident. Despite the renal tumors are of rare occurrence in dogs, this possibility should be considered in the differential diagnosis of animals with palpable mass, progressive weight loss and anorexia, especially in the age group of occurrence for such cancers. The ultrasonography of great value in determining the location of the mass and conclusive histopathologic classification of the tumors.