Abstract: The ocean is rich in microbial resources. It is an important direction to isolate and identify microorganisms from the ocean and develop applications. Luminescent bacterium JXLB was isolated from the surface of mullet captured offshore by using the streak-plating method. Its classification was conducted via culture characteristics,Gram staining, physiological and biochemical characteristics analysis and 16 S rRNA gene sequence analysis. Its application in water quality monitoring was explored. The results showed that JXLB was suitable for living in a low-salt environment（1%～3% NaCl） and could grow and emit light at 18 ℃～28 ℃, and the strongest fluorescence intensity was at 24 ℃. JXLB was Gram-negative bacilli with flagella, and showed positive reactions in motility,oxidase, V-P test, amylolysis, methyl red assay. JXLB can ferment glucose, sucrose, and glycerol to produce acid.The sequence of 16 S rRNA gene analysis showed that JXLB had a homology of 99.8% with Photobacterium carnosum. The phylogenetic tree proved that JXLB formed a branch with Photobacterium carnosum, which confirmed that JXLB belonged to Photobacterium carnosum. Furthermore, we found that the luminescence intensity of JXLB was correlated with the concentration of harmful substances in water and can be applied to rapid detection of water quality. In summary, the isolated luminescent bacteria JXLB belongs to Photobacterium carnosum, and can be used as indicator bacteria in water quality monitoring.