Abstract: In order to det ermi ne the cause of Hippocampus erectus suddenly death, we isolated a dominant bacterium SZVA20190621 from the diseased part of it, and then studied the morphological characteristics, physiological and biochemical characteristics, regression infection, 16 S rRNA gene evolution and drug sensitivity. The results showed that the strain produced glucose, mannitol, Trehalose anhydrous sucrose, oxidase activity and MR test were positive for physiological and biochemical identification; had 98.16% homology with Vibrio alginolyticus KT986151 on NCBI. Regression infection test showed that the strain SZVA20190621 was pathogenic to Hippocampus erectus, and its LD50 was 3.73×105 CFU/mL. In summary, the strain was identified as a pathogenic Vibrio alginolyticus. The results of drug susceptibility test showed that the strain was resistant to cefazolin,cefalotin, piperacillin, spectinomycin, amikacin, clarithromycin, clindamycin and furadantin; moderately sensitive to aztreonam, cefoxitin, cefatriaxone, kanamycin and erythromycin; highly sensitive to 17 different antibiotics such as ceftazidime, cefotaxime, cefoperazone, cefepime, streptomycin, tobramycin, gentamycin, bactrim and chloramghenicol. This study will provide some reference basis for the prevention and control of disease induced by Vibrio alginolyticus in Hippocampus erectus culture.