Granulosa cell tumor of the ovary is a rare form of ovarian cancer in children. An 11-year-old girl was admitted with complaints of galactorrhea and abdominal mass. Abdomino-pelvic ultrasound and computed tomography revealed an ovarian tumor. Her prolactine and estradiol levels were increased but luteinizing hormone and follicle-stimulating hormone were decreased. An exploratory laparotomy revealed a giant solid mass, which was completely removed and determined as juvenile granulosa cell tumor. The clinical, hormonal, and radiological findings and the therapy of galactorrhea associated with granulosa cell tumor in a child are discussed. To our knowledge, this is first time it has been described in childhood.