Objective Proteus mirabilis was isolated from the intestines of introduced cynomolgus monkeys and identified and tested for drug sensitivity to provide theoretical and technical support for detecting microorganisms from introduced experimental monkeys and to conduct breeding management and disease control. Methods Fecal samples were collected from cynomolgus monkeys via anal swabs, and bacterial isolation and culturing, biochemical identification, drug sensitivity tests, and mouse pathogenicity tests were performed. Results Suspicious bacteria were isolated from 8 of 60 cynomolgus monkeys and identified as Proteus mirabilis, indicating a 13. 3% infection rate of Proteus mirabilis in these monkeys. Susceptibility tests of this bacterium showed that it was highly sensitive to ceftriaxone, cefotaxime, cefoperazone, cefazolin, and penicillin; moderately sensitive to amikacin, gentamicin, ampicillin sodium, and furantoin; sensitive to norfloxacin and tetracycline; lowly sensitive to bacitracin, ciprofloxacin, kanamycin, and lincomycin; and resistant to furazolidone. Mouse pathogenicity tests showed that the isolated strains were highly pathogenic to mice. Conclusions The Proteus mirabilis infection rate was relatively high in cynomolgus monkeys. This bacterium was sensitive to cephalosporin antibiotics; therefore, cephalosporins can be used to clinically treat infections with this bacterium. Proteus mirabilis is highly pathogenic and potentially harmful to cynomolgus monkey populations and should be considered in their normal breeding management.