To explore the effect of sodium bicarbonate on expression of virulence genes from Aeramonas hydrophila, the relative expression levels of three major virulence genes, including hemolysin gene (AHH-1), aerolysin gene (AerA), and elastinase gene (ahyB) in A. hydrophila growing with sodium bicarbonate at 0.024, 0.048, 0.072, 0.096 and 0.120 mol/L were analyzed by fluorescent quantification PCR technique and compared with those of A. hydrophila without sodium bicarbonate as control. The result revealed that the expression levels of AHH-1,AerA and ahyB in A. hydrophila growing with sodium bicarbonate were significantly lower than those of A. hydrophila without sodium bicarbonate. With increasing sodium bicarbonate level, the expression levels of these genes showed a decreasing trend. The results of artificial infection indicated that compared with the A. hydrophila without sodium bicarbonate, median lethal dose of A. hydrophila with sodium bicarbonate was much higher. What's more, with increasing sodium bicarbonate concentration, the median lethal dose of A. hydrophila had a trend to increase gradually, and this means that the virulence of A. hydrophila decreased gradually.