Myomatous erythrocytosis syndrome (MES) is a rare gynecological condition, defined by the presence of the clinical triad of erythrocytosis, uterine fibroids, and normalization of red blood cell counts after the surgical removal of uterine fibroids. Herein, we report the case of a woman, in the postmenopausal stage, with the clinical triad of MES. She had a history of erythrocytosis of unknown etiology and underwent phlebotomy for a year prior to visiting our hospital. Pre-operative hemoglobin (Hb) level, hematocrit (Hct) level, and red blood cell (RBC) count were 18.1 g/dL, 56.1%, and 6.52 million cells/μL, respectively. She underwent exploratory laparotomy, transabdominal hysterectomy, and bilateral salpingo-oophorectomy. The operative findings revealed a large uterine myoma, and the pathology result was compatible with uterine leiomyoma. All hematologic parameters returned to the normal range on post-operative day 1. Her hematologic parameters returned to normal values 4 weeks after surgery with a Hb level of 13.5 g/dL, Hct level of 41.2%, and RBC count of 4.92 million cells/μL. The exact pathophysiology of this condition remains unknown. However, surgical removal of uterine myoma is the mainstay of treatment. Despite the rarity of this condition, its diagnosis should be considered in patients presenting with erythrocytosis and uterine masses.