A 56-year-old woman was admitted to our hospital for treatment of non-specific interstitial pneumonitis (NSIP). The patient started prednisone treatment, but one month later treatment with voglibose, an alpha-glucosidase inhibitor (alpha-GI), was started because of prednisone-induced diabetes mellitus. One week later, a massive volume of free air below the diaphragm was detected by a chest X-ray examination. An abdominal CT examination demonstrated pneumatosis coli and the patient was diagnosed with pneumatosis cystoides intestinalis (PCI). Voglibose was discontinued and parenteral nutrition and oxygen inhalation were initiated. Radiographic findings of PCI disappeared within 7 days. We encountered a rare case of PCI, that was associated with alpha-GI treatment.