Leiomyomas are common benign uterine tumors. However, the incidence of vaginal myoma is very rare and may be confused with a variety of vaginal tumors. We report a case of 43-year-old nulligravida who presented with a protruding painful vaginal mass for 7 days. The mass had initially appeared 3 years prior, as 2 to 3 cm that had not subsequently increased. However suddenly, there was rapid severe enlargement over the course of 7 days. Physical exam revealed a monstrous shaped, black color with focal necrosis, odorous protruding vaginal mass about 7 cm in size. The vaginal mass was infected and degenerated. And vaginal wall was also destroyed by the enlarged mass. Because of the clinical features and radiologic findings, the preoperative diagnosis was a vaginal malignancy. We reported an extremely rare case of vaginal myoma that had several characteristics of malignancy, with a brief review of the literature.