An 11-year-old poodle bitch was presented for investigation of multicentric mammary masses. Abdominal sonography and radiography demonstrated abnormal enlargement of uterus and ovaries. Blood analysis revealed high progesterone concentration. The ovariohysterectomy and mastectomy were performed. Histopathologically, the mammary masses revealed complex carcinoma-tubulopapillary carcinoma with papillary pattern and tubule pattern. In the uterus, cystic endometrial hyperplasia was observed. Scattered inflammatory cells were observed in the endometrial stroma and mucinous material was protruded from endometrial surface. Also, in the ovaries, bilateral ovary granulosa cell tumor was detected. The bitch made a complete recovery following the ovariohysterectomy and mastectomy. This case was a very rare multiple tumor occurrence with bilateral ovary granulosa cell tumor and mammary complex carcinoma. High progesterone concentration was characterized clinically in the bitch.