Clostridium symbiosum was isolated from the blood of a 61-year-old immunocompromised woman who had diagnosed ovarian cancer with multiple metastases and who had developed persistent tachycardia. A blood culture was drawn from the peripherally inserted central catheter, and non-spore-forming gram-negative rods were detected in an anaerobic vial. The organism showed tiny and pinpoint colonies and was unidentified by Vitek II (bioMerieux, France). The 16S rRNA gene sequence showed a 99.4% identity with C. symbiosum. To our knowledge, this represents the first report of C. symbiosum isolation in Korea. (Korean J Clin Microbiol 2010;13: 90-92)