Ovary juvenile granulosa cell tumors (JGCT) are rate sex cord-stromal tumors that are most commonly encountered in prepubertal girls: These tumors can be of the adult type (95%) and juvenile type (5%). The main causes of complaint are abdominal distention and abdominal pain. Definitive diagnosis is confirmed by histopathologal and immunohistochemical examinations. A 10-year old girl presented with massive abdominal distention, acute abdomen findings and ascites. Abdominopelvic magnetic resonance imaging showed masses with multiple cysts and solid components in the left ovary. Tumor markers were normal, but serum estradiol level was elevated. The patient Underwent mass resection with left salpingo-oophorectomy and total omentectomy. Final histopathological diagnosis was JGCT. We herein reporte an extremely rare case of advanced stage JGCT causing massive ascites and acute abdomen.