We reporta testicular jevenile granulosa cell tumour (TJGCT) with characteristic clinical and histopathological features. The tumor was present in the left abdominal testis of a 7-month-old infant with a 45,X/46,XY karyotype and ambiguous genitalia. Preoperatively, the infant was diagnosed as having functional testicular and ovarian elements based on elevated levels of serum testosterone and estradiol following human chrionic gonadotropin and human menopausal gonardotropin administration, respectively. Histologically, the gonad contained a tumorous lesion composed of an admixture of cellular areas and multiple cystic follicles that had some continuity with the adjacent testicular tubules. Some tumor cells showed immunoreactivity for estradiol. The right gonad was a streak gonad containing small irregular nests of sex cordtype cells. No maturing ovarian follicle was present in eith gonald. To our knowledge, this is the fifth reported case of T-JGCT with abnormal sex chromosomes, and the first case of T-JGCT confirmed to have not only the morphological but also the function charactersitics of granulosa cells.