Clostridium sordellii is a gram-positive spore forming anaerobic bacillus, rarely encountered in human infection. It produces several exotoxins which contribute to myonecrosis, pulmonary infection, obstetric infection and bacteremia. C. sordellii bacteremia is very rare and has been reported in few patients with malignancy or immunosuppression. To date, there has been no report in Korea. Mortality is high when deep site infection exists regardless of underlying pathology and immune status. In contrast, superficial skin and subcutaneous tissue infection has a favorable prognosis. We present a case of C. sordellii bacteremia in a patient with osteosarcoma. The patient was admitted for the treatment of the infection at the ulcerative osteosarcoma lesions of the leg, and C. sordellii bacteremia was demonstrated. He was successfully treated with intravenous ampicillin/sulbactam for two weeks.