Bacteriocin produced by Lactobacillus acidophilus was tested for it's potential as aprobiotic cullure, it's exhibited good sensitivity to heat, pro- tease enzyme, acid tolerance, as well as bile resistance in media containing 0.3% bile acids. Bacteriocin was active over wide pH range and inhibited a number of pathogenic bacteria. The SDS - PAGE of the active fraction resulted in a single band with molecular mass of 5.4 KDa. In challenge test. Mice that were fed on milk based diets contain bacteriocin (10⁸ C.F.U).showed 100%. protection level . Meanwhile the antibody titers in the serum of immunized mice with bacteriocin were significantly higher than the titers in the control of unprotected_. mice . These results confirmed the probiotic effect of bacteriocin against colonization of most microorganism in the animal tissue as well as enhancing their immune response.