Isosexual precocious puberty in girls has several etiologies. Juvenile granulose cell tumor is one of the rarest causes that only stands for 1.5% of ovarian cancers. This tumor mostly encounters in first 2 decades of life. This paper is a report of an 8-year-old girl with precocious puberty that within five months developed breast enlargement followed by menarche. Works which are done to find the underlying cause of precocious puberty revealed juvenile granulosa cell tumor in her left ovary. She then under went laparoscopic surgery and 3 courses of chemotherapy. She did not experience any vaginal bleeding after that and the serum level of estradiol lay among its normal ranges, but after that the tumor relapsed and presented as abdominal pain and a huge mass which under went resection of all afflicted tissues. After 2 courses of chemotherapy, her status deteriorated and unfortunately she died after 6 months from the time of diagnosis. Treatment for this disease is consists of resection surgery and chemotherapy. If this tumor is diagnosed in its early stages, it will be curable, but in its advanced stages, up to 80% of patients die from recurrent tumors. The reported patient was diagnosed at stage IIIC that had poor prognosis.