Nowadays consumers are increasingly demanding food that is free from pathogens with minimal processing and fewer chemical preservatives but with an unimpaired sensorial quality and maximal shelf-life. Various suggestions are presented to achieving this aim and most of them are implying to biopreservation. Biopreservation has gained increasing attention as means of naturally controlling the shelf-life and safety of foods with organisms especially microorganisms or their products. In the food industry, Lactic acid bacteria (LAB) are widely used as starter cultures. LABs have some advantages that nominate them as a good choice for using in biopreservation. They have an important role in the inhibition of food-borne pathogenic and spoilage microorganisms with antimicrobial metabolites. They produce different antimicrobial components in their defense system including lactic acid and other organic acids, hydrogen peroxide, di-acetyl, CO 2 and bacteriocins. Bacteriocins are ribosomally synthesized peptides or proteins usually antagonistic to closely related bacteria to producer. Since bacteriocins produced by LAB are considered to be Generally Recognized as Safe microorganisms, they are receiving much attention. At the first part of our study, we compared 3 methods used for measuring bacteriocinegic activity of LABs including Spot on the lawn, Agar well diffusion assay (AWDA) and Photometric assay (PA). We showed Spot on the lawn method was introduced as more reproducible, rapid and easy to score than Agar well diffusion and Photometric assay. Also, the Photometric assay is more accurate than other 2 methods. At the second part of our study, 42 strains of lactobacillus delberueckii su. bulgaricus that had been isolated from conventional yoghurt were screened in terms of bacteriocinegic activity by Spot on the lawn method, and K41 strain showed the most inhibition activity against indicators ( Listeria monocytogenes and Escherichia coli O157:H7). As most of the Bacteriocin like substances secreted by LAB`s are secondary metabolites, the antimicrobial activity of the component released by K41 was initially detected in the late exponential phase of growth and the maximum levels of antimicrobial activity were found at the stationary phase. This antibacterial peptide was extremely heat-stable (15 min at 121 ?C ) and was active over a wide pH range (pH=2-10). It was found to be sensitive to proteolytic enzymes (trypsin, pepsin, and proteinase K) but resistant to amylase and lipase, also the mode of its action was identified as bactericidal. The inhibitory spectrum of this peptide was tested against 10 food-borne pathogenic and spoilage microorganisms including 5 G + and 5 G - bacteria and it exhibited a narrow range of inhibitory activity against G + bacteria with extremely anti-listerial activity; on the other hand it was almost ineffective against G - bacteria. In addition, this study showed that non-ionic detergents (Tween-20, Tween-80 and Triton X100) had no effect on antimicrobial activity of produced peptide. To our knowledge, this Bacteriocin Like Inhibitory Substance (BLIS) is related to left; MARGIN: 0in 0in 0pt; unicode-bidi: embed; DIRECTION: ltr" align=left Keywords: Biopreservative, Bacteriocin, Lactobacillus bulgaricus , Screening, Characterization