A male patient in his 80s visited our hospital for cough and abdominal pain. Further examination revealed a markedly enlarged bowel and urinary bladder and hepatic portal venous gas (HPVG). No sign of bowel ischemia or necrosis was observed. Therefore, he was treated conservatively. Computed tomography performed after 13 h revealed no HPVG following bowel decompression. Hence, we concluded that HPVG was induced by high gastrointestinal luminal pressure. The patient was discharged on the 28th day after admission. Thus, when patients present with HPVG with an enlarged bowel, they can be conservatively treated if the following conditions are met: 1) no sign of bowel ischemia and necrosis, 2) no peritonitis, and 3) no shock state.