Twenty apparently healthy Newzealand white male rabbits (average weight – 818.3 + 12.8 grams) were divided into four groups (five animals each). The first group was served as the normal control, the second group was orally administered with 2mg Dimethyl Diphenyl Bicarboxylate (DDB)/kg b.w. for 28 successive days, the third group was twicely vaccinated ( two weeks apart) with pasteurella multicida (sero var 5 : A) vaccine, and the fourth group was vaccinated also (as in the third group) along with DDB treatment (as in the second group). At the 29th , day ( 21 day s post second vaccination) the blood, serum, spleen and liver sample were obtained from all animals. The hematological, serological, serum protein electrophoretical, biochemical and histopathological studies were carried out. Results indicated that DDB treatment induced immunostimulant activity due to the significant increase in the total immunoglobulin's (Gamma- globulins), lymphocyte percentage and prominent lymphocytic aggregation within the lymphoid follicles of the spleen, but the increase in the indirect Haemagglutination specific antibody titer by DDB treatment was non-significantly against pasteurella multocida vaccine, also the DDB induced significant inctease in red blood corpuscles and hemoglobin concentration and reduced ALT-enzyme activity with the improvement in liver histology in vaccinated rabbits compared to the only vaccinated animals. Based on our study. It should be considered to the only vaccinated animals. Based on our study. It should be considered that DDB as a promising immunostimulant. Blood tonic and hepatoprotective drug.