Spontaneous bacterial peritonitis (SBP) is a life-threatening complication of liver cirrhosis. Recently, rifaximin, a non-absorbable antibiotic which is used to prevent recurrent hepatic encephalopathy, has been proposed as effective prophylaxis for SBP. Here, we present an unusual case of SBP under treatment with rifaximin. A 50-year-old woman with liver cirrhosis was admitted because of tense ascites and abdominal pain. She was under long-term oral prophylaxis with rifaximin due to hepatic encephalopathy. Paracentesis revealed SBP caused by Pasteurella multocida, which was sensitive to multiple antibiotics, including rifaximin. Treatment with ceftriaxone resulted in rapid resolution of the peritonitis and restoration of the patient. Since P. multocida is usually transmitted from pets, the patient's cat was tested and could be identified as the most likely source of infection. This case should elicit our awareness that uncommon pathogens and unusual routes of transmission may lead to SBP, despite antibacterial prophylaxis with non-absorbable antibiotics. Nevertheless, such infections may still remain sensitive to systemic therapy with conventional antibiotics.