In this study, we have for the first time isolated Aeromonas salmonicida strain XJ-JT from Yangtze finless porpoise which showed clinical symptoms such as ulcers and rotten skin. We found that the strain XJ-JT was a gram-negative bacterium with blunt ends and non-sporulating; 16S rRNA gene fragments of of several strains were amplified and sequenced, and phylogenetic trees were constructed which reveal the similarity with Aeromonas salmonicida isolated from Silver carp. Moreover, we studied its biological characteristics by performing physicochemical characterization, genetic evolution analysis, drug susceptibility assays and a pathogenicity test. 20 common antibiotics were tested in drug susceptibility assays. We showed that XJ-JT is highly sensitive to cefotaxime sodium,  ceftriaxone sodium and kanamycin, moderately sensitive to cefotaxime sodium, ceftriaxone sodium and kanamycin, and not sensitive to amoxicillin, ampicillin, tetracycline, and so on. An in vivo infection assay showed that this new strain, XJ-JT, has a strong pathogenicity in Crucian carp.