Abstract: The strain FZ01 was isolated from a diseased Anguilla Anguilla taken from a fish farm suffering from an outbreak of unknown pathogen.The virulence,morphological,physiological and biochemical characteristics and serotype of the FZ01 were investigated.Oxidase test,catalase test and a glucose fermentation test were done by A VITEK automatic microbiological identification analysis.The results showed that the strain FZ01 was pathogenic for both eel and mouse.The fatality rate of 2107CFU for eel was 100% in 48 h.It was confirmed as the causative agent of the epidemic.FZ01 was Gram-negative bacilli,and the results showed that it was Aeromonas hydrophila.Tests of the pathogens susceptibility to antibiotics demonstrated its sensitivity to Enrofloxacin,tetracycline,and ciprofloxacin,but resistance to amoxicillin and sulfamethoxazole.Serologic tests showed that this strain's cell agglutination titer with the Fujian Province serotype O∶Ah10501 was 1∶27.These results suggested that we should take full account of serotype features in disease control process,and select the appropriate drugs and immune agents.