Pneumatosis cystoides intestinalis (PCI) is a rare disease characterized by the presence of intramural gas-filled cysts in the gastrointestinal wall. This disease has been documented in patients with various medical conditions such as gastrointestinal disease, chronic obstructive lung disease, sepsis, and autoimmune disorders. A 49-year-old woman, who was undergoing immumosuppressant therapy due to polymyositis, developed PCI. She experienced a gradual onset of abdominal distension. A simple abdominal radiograph revealed small, round air shadows involving the small bowel, and abdominal computed tomography showed intraluminal air bubbles at the jejunal loop with free air in the peritoneum. Treatment with doxycycline effectively relieved the clinical symptoms and reduced the intramural gas.