A 7-year-old, female Shih-tzu dog with clinical signs of hematuria, oliguria, stranguria was brought to the Veterinary Teaching Hospital, Chonnam National University. Ultrasonography revealed the left hydroureter, hydronephrosis and urinary bladder mass ($12.1;{ imes};22.0;mm$). The dog was finally diagnosed as the secondary unilateral obstructive uropathy by urinary bladder mass. The treatment such as unilateral nephroureterectomy and chemotherapy using piroxicam were performed to the dog. After 8 months of treatment, the polyp was not detected by ultrasonography. We concluded that urinary bladder mass was cured completely.