Granulosa cell tumours (GCT) are uncommon sex cord-stromal tumours of the ovary, and comprise approximately 2-3% of all ovarian malignancies. These tumours characteristically have a low malignant potential, and have slow growth rates. They are hormonally active stromal cell neoplasms that can secrete sex steroids such as estrogen. Serum tumor markers such as estradiol and inhibin are used for diagnosis of GCT. Low serum level of FSH may be useful as a diagnostic marker in postmenopousal period. Patients may present with vaginal bleeding caused by endometrial hyperplasia or uterine cancer as a result of prolonged exposure to tumor-derived estrogen. In this case report, a patient with a painless mass of right ovary and atypical endometrial hyperplasia was presented. Frozen examination of the removed right ovarian mass revealed the diagnosis of granulosa cell tumor.