Hafnia alvei is a gram-negative bacillus that is rarely isolated from human clinical specimens and is rarely pathogenic. This organism is an extremely uncommon cause of spontaneous bacterial peritonitis (SBP). We report a case of an 83-year-old male with hepatitis C-associated liver cirrhosis and hepatocellular carcinoma who was diagnosed with SBP caused by H. alvei. He was admitted to an university-affiliated hospital with fever and abdominal pain. There were 2 episodes of SBP during 2 months. Although isolates of H. alvei from ascitic fluid were shown to be susceptible to cefotaxime, responses for cefotaxime treatment were inadequate in both episodes. Therefore, cefotaxime was switched to imipenem in the first episode and to ciprofloxacin in the second, according to the results of antimicrobial susceptibility. After the antibiotics was changed, SBP was resolved.