A 66-year-old woman 0 para 0 gravida complained of severe acute abdominal pain. Computed tomography revealed a moderately large and monotonous solid pelvic mass. Emergent laparotomy was performed. The mass had thin but twisted pedicle which seemed to arise from anterior lobe of left broad ligament. Histologically, resected tumor showed so called “patternless pattern” obviously. Further immunohistochemical analysis indicated negative CD34, CD117 and positive calretinine and cytokeratin staining, which suggests that tumor was originated from mesothelium, and we diagnosed as peritoneal fibrous mesothelioma. She had no residual tumors and she has no signs of recurrence for 24 months without any additional treatments. This is the extremely rare case of peritoneal fibrous mesothelioma found by acute abdomen due to twisting of its pedicle. As far as our knowledge, this is the first case of peritoneal fibrous mesothelioma found by acute abdomen.