A 26-year-old Japanese woman was admitted to the hospital because of fever and general fatigue. A diagnosis of acute hepatitis B was given because of high levels of transaminase and positivity for HBs-Ag, HBe-Ag and HBc-IgM. On the 2nd day progression to fulminant hepatitis was suspected, and steroid pulse therapy, cyclosporin, entecavir, and interferon-β were started. Her laboratory data improved until transaminase showed an increase on 18th day, and steroid was once again administered. Abdominal CT scan and plain abdominal X-ray showed pneumatosis cystoides intestinalis (PCI) mainly along the ascending colon without any symptoms. After discontinuation of steroid therapy, abnormal gas gradually disappeared. This is a very rare case of PCI, which may have been caused by short-term steroid pulse therapy.