Abstract: An experiment was performed to evaluate the effects of dietary supplementation of probiotic (Biosof®) and prebiotic (Active-Mos®) on broiler performance, organ weights, blood parameters and antibody titers against Influenza and Newcastle. Three hundred twelve 7-d-old male broiler chicks were randomly assigned to one of 3 dietary treatments for 6 weeks. The dietary treatments were: (1) control diet (without additive), (2) control diet plus probiotic (0.1% of Biosof®)/ton of feed), (3) control diet plus prebiotic (0.1% of Active-MOS/ton of feed). Overall body weight and feed conversion ratio were significantly (p<0.05) improved by dietary inclusion of the probiotic and the prebiotic compared with the control diet. The relative weights of duodenum, jejunum and ileum were greater (p<0.05) for probiotic-fed birds than the control group, however, duodenum relative weight in the prebiotic group was also significantly greater than control group. The serum concentration of cholesterol was lower in the probiotic fed group than prebiotic and control groups. The serum concentrations of total protein, albumin, globulin and albumin/globulin ratio were not affected by dietary treatments. The number of heterophils, monocytes, lymphocyte, eosinophils were not affected by dietary treatments. However, the heterophils to lymphocyte ratio was lower in the probiotic group than prebiotic and control groups. Serum antibody titers against Newcastle was higher in probiotic treatments compared with prebiotic and control groups, but no significant changes were observed in the antibody titers against Influenza. The results of this study suggest that the probiotic and prebiotic can be used as an alternative to antibiotic growth promoters in broiler diets and can improve the immune response to some vaccines.