Spinibarbus sinensis Bleeker in the Yangtze River and its tributaries is of great economical value. However， it suffers from serious diseases， particularly a bacterial disease named “muscle ulceration” in intensive aquaculture. In order to effectively control the disease of S.sinensis， it is necessary to clarify the changes of immune parameters of periphery blood in S.sinensis immunized with a kind of dead bacteria. One hundred and eighty healthy fish (S.sinensis) with an average body weight of (100±25) g were divided randomly into immunized and control groups. Each individual was intraperitoneally injected with 0.2 mL 1.0×10⁸ mL formalinkilled Aeromonas sobria in immunized group，and with 0.2 mL 0.65% sterile saline solution in control group. Then，approximate 2 mL of blood was taken from each fish caudal vein on Day 0，1，2，4，7，14，21，28 and 35 post injection to study the changes of immune parameters，such as haematocyte number，differential leucocyte count(DLC)，serum antibody titer，phagocytic activity of phagocytes and serum protein content. The results were as follows：the number of erythrocytes and leucocytes in peripheral blood of immunized S.sinensis increased during the first 4 days post injection and peaked on 4th day，then，gradually decreased to the control level(Fig.1a & 1b). The differential leucocyte count(DLC) of the immunized group increased and was significantly(or very significantly) higher than that of control group for monocytes and neutrophils from day 4 to day 7(Fig.2a & 2b)，and for lymphocytes from the 14th day to 28th day(Fig.2c)，but lower than that of control group for thrombocytes on day 4 and 21(Fig.2d)，and was the same level as that of control group for the four kinds of cells at the other sampling times. The phagocytic percentage(PP) and phagocitic index(PI) of phagocytes in immunized S.sinensis were significantly higher than those of the nonimmunized fish between day 2 and day 7，and of the maximum value on day 4，but were not significantly different from those of the nonimmunized S.sinensis at the other sampling times(Fig.3a & 3b). The serum antibody titers gradually increased in immunized S.sinensis during the first 21 days post injection and reached the greatest value on day 21，then，gradually dropped off，but always kept the low level of 1∶4-1∶5 in the nonimmunized fish(Tab.1). The serum globulin content gradually increased in the immunized fish from day 4 to day 21， peaked and significantly higher than that of the nonimmunized fish on day 21(Tab.2). The serum globulin changes resulted in the same change model of serum total protein，which was not of significant difference between immunized and control groups(Tab. 2). However，the serum albumin quantity was not significantly different between the immunized and control groups，and fluctuated a little in the two groups(Tab.2). Relative percent survival was 65.21% for the immunized S.sinensis after challenge by means of injection with 0.2 mL live A.sobria at a concentration of 5.0×107 mL for every individual(Tab.3). This indicated that the formalinkilled Aeromonas sobria(F_AS) stimulated S.sinensis to produce a significantly protective immunity against the pathogen bacteria infection. All the results stated above suggested that the vaccine(F_AS) made S.sinensis enhance the nonspecific cell immunity，such as monocytes，neutrophils and erythrocytes，during the early period(from day 1 to day 7)，and the specific cellular and humoral immunity，such as lymphocytes and antibodies，during the later period against the bacterial pathogen infection post single dose immunization，and the relative percent survival reached 65.21% for the immunized S.sinensis after challenge with live A.sobria.