To survey antimicrobial resistance,plasmid fingerprinting and relationship between the size of plasmids and resistance in Aeromonas hydrophila strains which were isolated and collected from fish at different time and in different areas in China.Antimicrobial susceptibility of 40 strains to 29 different antimicrobials were tested by K-B;plasmids DNA were obtained by alkaline lysis and digested by EcoRⅠand HindⅢ,plasmids elimination were treated by EB,then analyzed by agarose gel electrophoresis.Results showed that Aeromonas hydrophila exhibited high antimicrobial resistance,almost was multi-drug resistance;Out of 40 strains,15 strains(37.5%)contained plasmids;The relationship between the antimicrobial resistance and plasmid fingerprinting showed that the number and size of plasmids the strain carried had no significant correlation with its antimicrobial resistance.Plasmid fingerprinting indicated that the strain with the same source and similar antimicrobial resistance would have similar plasmid profile and macrorestriction map.The rate of plasmid elimination for 15 isolates was 100%,but partially eliminated;meanwhile,the resistance phenotype of 12 isolates partially disappeared,suggesting that plasmid and chromosome encoding the resistance genes,2.01 kb plasmid was associated with the resistance to Nalidixie acid and Vancomycin.