The findings and the role of fluorine-18-fluorodeoxyglucose positron emission tomography/computed tomography ((18)F-FDG PET/CT) for the diagnosis of ovarian granulosa cell tumor (OG) are described. We present the pre-operative findings of (18)F-FDG PET/CT scan of a case of OG concurrent with endometrium cancer and endometrial hyperplasia, which revealed a 48mm mass demonstrating mild increased metabolic activity on the right ovary. Total abdominal hysterectomy and bilateral salpingo-oophorectomy was performed. Frozen and paraffin-enbeded sections showed an encapsulated OG. There were few mitoses. There was concurrent atypical endometrial hyperplasia. In conclusion, we reported a case of an encapsulated OG, which showed mild uptake of the (18)F-FDG with concurrent endometrial cancer. There has been only one report of (18)F-FDG findings in primary ovarian granulosa cell tumor, similar to ours.