We reported a case of 72-year-old man who developed hyper-inflammatory state and multiple organ disorders without any apparent origin after off-pump coronary-artery bypass grafting (CABG), and who was treated with high-dose methylprednisolone successfully. Administration of high-dose corticosteroids for critically ill patients is not supported now, but this case showed prompt recovery after administration of steroid, so the treatment was thought to be effective. The patient was admitted to the emergent department in our hospital because of worsening angina pectoris. His past medical history showed hypertension and previous smoking, CABG, and Y-graft replacement of abdominal aortic aneurysm. He was diagnosed that left internal thoracic artery (LITA) and saphenous vein graft (SVG) were stenotic and scheduled to undergo off-pump CABG with left thoracotomy due to the history of mediastinitis following previous CABG. The procedure was performed successfully, but he developed high-grade fever and significant leukocytosis, hyper-bilirubinemia, and acute renal failure. He did not show any signs of local infection or allergy, and the microbiological tests such as sputum, blood, and cerebrospinal fluid cultures were negative. Infectious endocarditis was excluded by transesophageal echocardiography and mediastinitis was also excluded by computed tomography. We admimistered 500mg of methylprednisolone for three days from the 12th postoperative day, and observed prompt resolution of high-grade fever, inflammation and multiple organ disorder. Since then steroid administration was tailored for 25 days in total, and he discharged from ICU on 42nd day. We speculated the administration of methylprednisolone was effective because of the prompt recovery and its dependence on steroid dose.