In childhood mature cystic teratomas are the most common type of ovarian germ cell tumors. Tumors of neuroepithelial origin are extremely rare in mature teratomas. To the authors' knowledge, this is the first case report oligodendroglioma arising in a mature cystic ovarian teratoma in children. A 13-year-old girl presented with a history of pelvic pain for 2 months. An ultrasound examination showed a monolateral multicystic, calcific ovarian mass, measuring approximately 6 x 5 cm, arising in the left over and adnexia, suggesting a teratoma. An exploratorative laparotomy and ooferectomy were performed. On histopatological examination, various samples from cystic areas had mature tissues from all 3 germ cell layers, including skin, bone, bronchial structures, and cerebellum. Sections from solid areas showed uniform population of monotonous, rounded cells with indistinct cytoplasm and having perinuclear halo (fried-egg appearance) on a fibrillary, neuropilic background. Microcalcifications as calcospherites were noted in the stroma. Based on the typical morphological features, the cased was diagnosed as mature cystic teratoma with low-grade oligodendroglioma. To the authors' knowledge, there are a few reports in the literature of an oligodendroglioma arising in an ovarian teratoma in adults and this presented patient is the first case in childhood.