Peritonitis is a common clinical problem in patients treated by peritoneal dialysis. The most common organisms causing peritonitis are Gram-positive (especially staphylococcus species). Peritonitis with Streptococcus agalactiae causes rare but often fatal infections in peritoneal dialysis patients. We present the case of a 39-year-old female peritoneal dialysis patient who had peritonitis due to Streptococcus agalactiae and the infection was successfully treated with intraperitoneal Cefazolin and Vancomycin. There were no further episodes of peritonitis during the six-month follow-up.