Based on the published 16S rDNA gene sequence of Aeromonas spp. and aerolysin gene sequence of Aeromonas hydrop hila, the synthetic oligonucleotide primers were used in a polymerase chain reaction ( PCR) technique to detect the gene for specific 16S rDNA and aerolysin of patho genic A . hydr ophila. A. hydr ophila can be clearly discriminated from the other Aeromonas species by 16S rDNA gene PCR, the detection limit for the aerolysin gene by PCR amplification was 1fg DNA. 36 strains were tested for pathogenic A. hydrophila by PCR method and pathogenic aeromonads diagnosis kit and their coincident rate was 94. 4%. The PCR can clearly identify A. hydrophila from Aeromonas species, and can identify aerolysin- producing strain of A . hydrop hila. In conclusion, this PCR- based method is rapid, sensitive and specific for the detection of pathogenic A . hydrophila, and it is a practical method for pathogenic A. hydrophila detection.