Hyperbaric oxygen therapy (HBOT) is now a commonly adopted therapeutic option for ileus and is reported to prevent endotoxemia. We had a case of septic shock, however, following HBOT in a patient with ileus. A 60-year-old male patient underwent HBOT after unsuccessful conventional therapies for ileus. He recovered from abdominal distention and, on the other hand, fell into shock with high fever after HBOT. Blood study at admission to ICU showed elevation of CRP and depletion of white blood cell and platelet, which implied sepsis and sepsis-induced disseminated intravascular coagulation. Antibiotics, gamma globulin, gabexate mesilate, and antithrombin III were administered. The patient got well by degrees during one week in ICU to return back to a ward. Serratia marcescens grew in blood culture. We suspect that septic shock was induced by bacterial translocation which has some relation with HBOT.