We describe a rare combination of Mayer-Rokitansky-Kuster-Hauser syndrome and immature teratoma of the ovary in a 4-year-old girl. The patient was admitted due to increased abdominal size. Sonagraphy and C-T scan revealed a heterogeneous mass with cystic, calcified, and solid parts. A right salpingo-oophorectomy was performed under the FIGO (International Federation of Gynecology and Obstetrics) staging of stage Ia. The diagnosis of immature teratoma, grade II, was confirmed by histopathologic examination. Agenesis of the upper third of the vagina and the uterus was also confirmed by the surgery.