To clarify the cause of mortality in Pelophylax nigromaculatus， a pathogenic bacterial strain designated B20200824 was isolated from the brain， spine， liver， and kidney of diseased P. nigromaculatus. The strain was identified through physiological and biochemical assays， 16S rRNA sequencing， and phylogenetic analysis.. Subsequently， the susceptibility and minimal inhibitory concentrations （MICs） were determined using the Kirby-Bauer （K-B） and broth micro-dilution methods， respectively. After identification， the strain was characterized as a Gram-negative short bacillus with biochemical properties consistent with those of Proteus vulgaris. Moreover， 16S rRNA sequencing and phylogenetic analysis revealed that the strain exhibited a close genetic relationship with P. vulgaris， which shared over 99% genetic homology. Consequently， strain B20200824 was identified as P. vulgaris. The results of the drug susceptibility test showed that the strain was resistant to norfloxacin， amoxicillin， enrofloxacin， and 3 other drugs； it showed intermediate resistance to doxycycline and erythromycin， and susceptible to azithromycin， cefotaxime， florfenicol， and 2 other drugs. The MIC of florfenicol was 0.25 μg/mL， while the MICs for imipenem， levofloxacin， and azithromycin were 0.125 μg/mL， and for cefotaxime it was 0.061 25 μg/mL， respectively. These results were consistent with those obtained from the susceptibility assay. Taken together， these findings demonstrate that P. vulgaris can cause disease in P. nigromaculatus， and florfenicol is recommended for controlling infections caused by P. vulgaris in clinical practice.