Peritonitis in peritoneal dialysis therapy is one of the important and life-threatening complications. Generally, gram-positive microorganisms cause peritonitis. Flavimonas oryzihabitans is gram-negative bacillus and rarely pathogenic. Particularly, it is an infectious agent in immunocompromised patients with a catheter in the body and has been reported as the causative agent of peritonitis in a few cases of peritoneal dialysis. In this report, we present a case of peritonitis due to Flavimonas oryzihabitans.