Aims: The main aims of this study were to clone and express an outer membrane protein (OMP), OmpW, of Aeromonas hydrophila and to study its distribution in Aeromonas spp. Methods and Results: The gene encoding OmpW in A. hydrophila has been cloned and expressed in Escherichia coli. Primers were designed for amplification of full-length ompW gene and used for identification of this gene in different Aeromonas spp. Of the 42 Aeromonas strains tested, all the isolates were positive by polymerase chain reaction (PCR) except one strain of Aeromonas veronii biovar veronii (VTE338). None of the other gram-negative bacteria were positive by PCR with primers specific to ompW gene of A. hydrophila. Polyclonal antibodies were raised in rabbit against the purified recombinant protein and the reaction of these antibodies was confirmed by western blotting using the purified recombinant protein and 42 Aeromonas cultures grown at various salt concentrations. Conclusions: The ompW-based PCR method developed in this study was found to be 100% specific and 97% sensitive. Expression of OmpW protein of Aeromonas was found to be salt-dependant. Recombinant OmpW protein was found to be highly immunogenic in fish. Significance and Impact of the Study: To our knowledge, this is the first report on cloning and expression of OmpW protein of A. hydrophila. Full-length ompW gene amplification by PCR can be used for the detection of Aeromonas. Recombinant OmpW protein can be useful for vaccination of fish against Aeromonas spp.