Despite significant advances in obstetric and pediatric health care, Streptococcus agalactiae(Lancefield group B β-hemolytic Streptococcus, GBS) remains one 91 the most prevalent and devastating pathogens in peripartum women and their newborn infants. It may cause urinary tract infection, chorioamnionitis and endometritis, bacteremia, and cesarean wound infection in the peripartum period. It was Pasteur who first identified microbes in the blood and lorchia of septic women. After that, in 1938 the isolation of S. agalactiae from three mortally ill women was reported, thereby implicating it as another cause of puerperal sepsis. S. agalactiae is now one of the most common causes of neonatal sepsis and meningitis in the United States. However, in Korea there have been only twenty-three cases of neonatal meningitis and/or sepsis due to group B β-hemolytic streptococcus reported. Recent studies have noted other serious infections in adults, including bacteremia, pneumonia, cellulitis, osteomyelitis, meningitis, and endocarditis. In Korean adults no case of pneumonia due to S. agalactiae has been reported till now. As minimal inhibitory concentration of penicillin was reported to be higher for S. agalactiae than for S. pyogenes, minimal inhibitory concentration of penicillin for S. agalactiae should be tested. Herein we describe the course of a case of S. agalactiae pneumonia and bacteremia in a 74-year-old diabetic man, and we review the literatures.