To clarify the roles of virulence genes and extracellular products played in the pathogen city of Aeromonas,PCR amplification,SDS-PAGE electrophoresis,plate diffusion and phylogenetic analysis were used in this study to investigate into the differences of extracellular virulence factors from 7 trains of pathogenic Aeromonasisolated from diseased eels. The results showed that these 7 strains were significantly different in the amount and types of virulence genes (hly,aer,ast,act,alt,ahpA,epr and exu),of which hly may be mainly responsible for the pathogenicity of Aeromonas. The extracellular products of the 7 Aeromonas strains were different in both the amount and types,but 5 strains contained an~50.7 ku protein which might be the product of aer gene. All the 7 Aeromonas strains exhibited hemolytic activity,protease activity of casein and lecithin in all the different growth phases tested,and their detectable activities were consistent with expression of virulence genes. Genes hly and ahp were highly conserved between genus,while exu was specific even within species.