Leiomyoma is benign mesenchymal tumor, that frequently occur in uterus but it rarely happens in ovary. Ovarian leiomyomas are seen concomitantly with uterine leiomyoma in about 78% of cases. They often discover incidentally but their most clinical manifestations are abdominal pain and palpable mass. Herein, we reported a large ovarian leiomyoma in a 22-year-old woman with abdominal pain and palpable mass at lower abdominal region. Computed tomography scan revealed large adnexal mass. Microscopic appearance was typical for leiomyoma but because its rarity in ovary the immunohistochemical staining was done. Major differential diagnostic considerations for this tumor in ovary are fibroma/thecoma, sclerosing stromal tumor, and leiomyosarcoma. The immunohistochemical staining with desmin, inhibin, and α-smooth muscle actin are helpful to rule out this differential diagnosis.