Teratomas are germ cell neoplasms originated from the ectoderm, mesoderm or endoderm. The dermoid cyst or mature cystic ovarian teratoma is a rare tumor in female-canine, which can cause serious damage to the fertility and health of animals. The present case reports an ovarian cyst as an intraoperative finding in a 5-year-old German Shepherd female dog. The patient presented purulent vaginal discharge during three weeks approximately. The clinical signs associated to ultrasound exam enabled confirming the diagnosis of pyometra, referring the patient to surgical treatment, by performing ovariohysterectomy. After exeresis of ovaries and uterus and at macroscopic inspection were perceived size and coloration abnormalities of the left ovary, finding, after incision, its interior filled by bristles and sebaceous material. The specimen was forwarded to histopathological analysis, confirming the diagnosis of dermoid ovarian cyst. It concludes that the lack of specificity of the primary signs hinds the clinical diagnosis, contributing to incidental findings of this alteration on abdominal surgeries and that the ovariohysterectomy is an effective treatment to this condition.