The patient was a 31-year-old woman, who was diagnosed as having systemic lupus erythematosus and administered 10mg/day of prednisolone. She was in pregnancy at 38 weeks. She was referred to the department of surgery because of the development of severe abdominal pain with muscle guarding and rebound tenderness. Ultrasonography revealed marked thickening of intestinal walls and a small amount of ascites. An exploratory laparotomy and caesarian section were performed. The operative findings revealed nonbacterial peritonitis with serous ascites and segmental edema of the small bowel, compatible with lupus peritonitis. According to review of the literature, pregnancy might be unlikely to a risk factor for lupus peritonitis. Surgeons should be aware of this condition and determine whether or not the symptoms require surgery without delay, so that both mother and child might not be catastrophic.