A 60-year-old man presented with a 1-day history of fever, vomiting, and diarrhea. He was diagnosed with severe septic shock on the basis of a body temperature of 38.9℃, heart rate of 92/min, respiratory rate of 25/min, WBC count of 22,970/μL, C-reactive protein (CRP) level of 136 mg/L, blood urea nitrogen (BUN) of 34.0 mg/dL, and creatinine of 2.98 mg/dL. On blood culture, Gram-positive cocci were detected in all 6 bottles. Small grayish non-hemolytic colonies were found on blood agar plates after incubation at 37℃ for 2 days. The isolates were negative for catalase and L-pyrrolidonyl-β-naphthylamide hydrolysis, and positive for bile-esculin and leucine aminopeptidase activity. The strain was identified as Streptococcus gallolyticus subsp. pasteurianus using Vitek 2 GP II systems. We performed 16S rRNA gene sequencing and detected 100% identity with S. gallolyticus subsp. pasteurianus strain CIP 107122^T (1,345/ 1,345-bp). The patient recovered after receiving ampicillin-sulbactam. This is the first report of phenotypic and genetic identification of S. gallolyticus subsp. pasteurianus causing severe septic shock in a Korean patient. (Korean J Clin Microbiol 2011;14:144-147)