Abstract: A pair of primers were designed according to the published nucleotide sequence of a putative outer membrane protein gene (omp) of Aeromonas hydrophila.With the specific primers, a target fragment about 1.1kb was amplified from Aeromonas hydrophila L316 via PCR.The target fragment was inserted into the linearized pGEM-T easy vector.After enzyme restriction and sequencing analysis, the nucleotide data had been further analyzed by DNA man and ClutalW software.The analysis results showed that the cloned DNA fragment had the longest open reading frame (ORF) of 1035nt, it predicted to be encoded a 344-AA protein with the molecular weight of 36kD.Hydrophobicity analysis suggested that the protein was highly hydrophilic, especialy at the first 24 amino-acid, this region could be function as signal peptide.The homologious comparison proved the cloned gene had 96% homology to the sequence of the omp gene, and the alignment of the amino acid sequence was 98 %.Campared with other amio acid sequences of outer membrane proteins, major outer menbrane protein of Aeromonas hydrophila L316 belongs to the ompA family.