Cystic changes of ovarian tissue are crucial as they cause infertility in laboratory animals. A 4 years old, weighing approximately 500 g adult, intact guinea pig had pruritic progressive alopecia over the flanks at the dorsal area and abdomen symmetrically, bilaterally for a month. Beside, an abdominal enlargement was observed outside on the guinea pig. Large polycystic ovaries were detected behind the kidneys during ultrasonography. Also abdominal radiography revealed the cystic structures at the same region. Ovariohysterectomy was performed on the animal, multiple thin walled, fluctuant fluid-filled, large cysts measured as 3.9x2.5 and 4.5x2.8 cm diameter were detected at the left and right ovary, respectively. The uterine body was observed normal macroscopically. The guinea pig was died after the operation during reanimation because of the hypothermia. The organ pieces were submitted to pathology for histopathological examination after the operation. Histologic examination demonstrated a diagnosis of serous multicystic papillary adenoma of the ovaries and glandular cystic hyperplasia of uterus. In conclusion, this case report describes the necessity of not to ignore the ovarian pathologies with guinea pigs demonstrate symmetric, bilateral alopecia on the skin and indicates the importance of postoperative care in laboratory animals despite a successful anesthethic choice and operation.