A female mixed miniature pinscher dog, about 5 years old, 4 kg, was referred to veterinary teaching hospital of Chungnam National University with chief complaint of excessive hemorrhagic vaginal discharge for a month, partial alopecia and hyperpigmentation. There are no specific change with CBC, blood chemistry and X-ray findings but we figured out high estrogen concentration with hormone analysis and detected a majority of the superficial epithelial cells with pyknotic nuclei by cytologic examination of vaginal smear preparation and multiple ovarian cysts on both ovaries by ultrasonography. Based on the clinical signs, hormone analysis, vaginal smear preparation and ultrasonography, the authors diagnosed this case as hyperestrogenism with ovarian cysts.