To examine the effects of vaccination against Babesia gibsoni infection in dogs, 15 normal mixed-breed dogs(5 month to 1 year old) divided into 3 groups with 5 dogs in a group. One of them was selected as control group(group A) and others were selected as experimental groups(group B and C). The group B was vaccinated with sonicated antigens and the group C was vaccinated with 0.2% of formalin treated antigens. The results obtained in the examination were summarized as follows : 1. In the western blot, the lane A revealed specific two bands on the regions of 54kd and 100kd, respectively. 2. After the first vaccination, the antibody titers of group B and C were higher 5 times(1 ： 200) than those of control group(1：40). After the second vaccination, the antibody titers of group B and C have not changed. When challenged with the protozoa(Babesia gibsoni), the antibody titers(1 : 5,000) were elevated in all groups. But these were not exceeded over 1 ： 5,000 for 4 weeks. 3. After challenge, the peak time of increased numbers of the protozoa was the 15th day (12-18 days) in all groups. During these days, the rate of parasitized erythrocytes in control group was 55.0${pm}$5.4%. But those of group B and group C were 26.0${pm}$6.4%, and 15.6${pm}$7.8％, respectively. 4. After challenge, all of the values of PCV, Hb, RBC were shown to decrease in all of the control and experimental groups. 5. The total leukocytes counts are shown a tendency of reduction in all groups after challenge. 6. In all groups, there were increase in lymphocytes and monocytes after challenge.