The isolation of Aureimonas altamirensis (a rare opportunistic pathogen with a yet unresolved pathogenicity) from the ascites fluid of a patient with bacterial peritonitis is reported. The strain was first identified by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) and the result was confirmed using 16S rDNA sequencing. An antimicrobial susceptibility profile was determined according to the European Committee on Antimicrobial Susceptibility Testing (EUCAST) guidelines published in 2013, revealing sensitivity to all antibiotics tested. The patient was treated effectively with levofloxacin.