The lipopolysaccharide (LPS) structures of strains of fish pathogenic bacteria; Vibrio anguillarum, Aeromonas hydrophila, Edwardsiella tarda, E. hoshinae, E. ictaluri, and Pasteurella piscicida, were analyzed by the silver staining method in polyacrylamide gel. The LPS profiles in V. anguillarum had differences depending on the serotyping groups A, B, C, D, E, F, G, H, and I. The LPS of the six strains of serotype A had the same electrophoresis pattern. The LPS structure also differed for the tested strains of A. hydrophila. Five types of LPS profiles were found in Edwardsiella tarda strains. LPS profiles of E. hoshinae and E. ictaluri were differed from those of E. tarda. There were identical LPS structures of Pasteurella piscicida strains isolated elsewhere.