Black carp（Mylopharyngodon piceus）were immunized with three vaccines (formalin killed Aeromonas hydrophila:F-AH，outer membrane protein:OMP and lipopolysaccharide:LPS).Then,the blood was taken from each fish caudal vein of all groups on day 1，2，4，7，14，21 and 28 post injection to study the related responses of immune parameters.The results were as follows:the number of erythrocytes and leucocytes in peripheral blood of fish immunized by three vaccines all increased during the first 4 days post injection,peaked on day 4.The differential leucocyte count (DLC) of fish immunized by three vaccines all increased and were significantly higher than that of control group for monocytes and neutrophils from day 4 to day 7，for lymphocytes from day 14 to day 28,and peaked on day 21.The phagocytic percentage(PP) and phagocitic index(PI) of phagocytes in fish immunized by three vaccines were significantly higher than those of the non-immunized fish between day 2 and day 7，with the maximum value observed on day 4.The serum antibody titers gradually increased in fish immunized by three vaccines during the first 21 days post injection,reached the greatest value on day 21，then gradually dropped off.The result of challenging with live Aeromonas hydrophila showed that black carp immunized by three vaccines had good relative percent survival(RPS).OMP had the highest RPS，which was 75.0％，followed by LPS(67.8％) and F-AH(50％).All the results suggested that three vaccines made black carp enhance immunity against the bacterial pathogen infection.