Abstract: The uptake of granular antigen was examined in Carassius auratus ibelio af ter bath administration of GFP..marked Aeromonas hydrophila strain 4332( Ah4332GFP ) by hyperosmotic infiltrat ion ( HI) and direct immersion ( DI) . Much more marked bacteria had been found in gills than that in skin and gut in both treatments throughout the experiment. Quantitative analyses indicated that the main site of antigen uptake were the gills in bothHI and DI treatments. In addition, the amount of marked bacteria in gills and skin had increased obviously after hyperosmot ic treatment , and gut also had increased bacteria during experiment of 10min, 30min and 120min with the exception of 60 min after immersion. It showed that hyperosmotic treatment facilitated antigen entrance in fish.