BACKGROUND Infectious aortitis has a poor prognosis and high mortality rate if untreated. Here, we report a case of rupture of infectious aortitis induced by methicillin-resistant staphylococcus aureus (MRSA). CASE REPORT An 83-year-old female patient was hospitalized due to continuous fever and diarrhea, which was diagnosed as colitis. The colitis was determined to have been induced by small vessel vasculitis upon histological examination. Fasting and central venous hyperalimentation using a peripherally inserted central catheter (PICC) were carried out for rest of the intestine. Swelling and pus were observed at the insertion site of the PICC. Since methicillin resistant staphylococcus aureus (MRSA) was detected in the culture of the pus and the blood, the patient was treated with vancomycin. After confirming that the blood culture became negative, prednisolone (PDL) was started as therapy for the colitis. Her diarrhea and fever improved. After vancomycin was stopped, MRSA-arthritis appeared. She suddenly died due to acute massive hemorrhage into the mediastinum and left thoracic cavity from the atherosclerotic ulcer of the thoracic aorta. It took 98 days from the first detection of MRSA in her blood to her death. We found gram-positive coccus in the ruptured aortic ulcer and we also detected MRSA gene by polymerase chain reaction in the ulcer. These results suggest that MRSA could colonize in the aortic ulcer during the MRSA-bacteremia and the MRSA could contribute to the vulnerability of the aortic wall. CONCLUSIONS After septicemia occurrs in an elderly person, the patient should be followed up by considering infectious aortitis, especially when the patient has several risk factors.