In order to study the immune responses and protective efficacy in Amur sturgeon (Aeromonas hydrophila to immunize healthy Amur sturgeon by peritoneal injection. We investigated the following immune parameters:peripheral blood cell count, differential leucocyte count, phagocytic activity and index, acid phosphatase activity, lysozyme activity, neutralizing antibody, and relative percentage survival. The numbers of erythrocytes and leucocytes in the peripheral blood of immunized fish increased rapidly and reached maximum values of (8.50 ±0.17)×10⁸/mL and (8.96 ±0.44)×10⁶/mL, respectively, at 4 d post-immunization. The percentages of monocytes and neutrophils reached maximum values of 10.50% and 15.53%, respectively, at 4 d post-immunization, and were very significantly higher than those of fish in the control groups ( < 0.01). However, lymphocyte percentage reached a maximum value of 73.51% at 21 d post-immunization. The phagocytic index and percentage of neutrophils were 4.53 and 30%, respectively, at 4 d post-immunization. The activities of lysozyme and acid phosphatase in serum reached peaks at 7 d and 14 d post-immunization, respectively. Neutralizing antibodies in the immunized fish reached 1:203 at 21 d post-immunization. When the immunized fish were challenged with live , the relative percentage survival of the immunized group was 76.84%. These results showed that the formalin-killed was able to elicit immune protection in Amur sturgeon, which lays the foundation for the further research on immunoprophylaxis against the diseases caused by infection in sturgeons.