Bacteriocin is a proteinaceous compound that has bactericidal action against microorganisms. Bacteriocins from lactic acid bacteria are very potential as natural food biopreservatives. The aim of the research was to know the infl uence of the growth medium; MRS, CMG, LTB and CM on antimicrobial activity of Leuconostoc mesenteroides Pbac1. Growth inhibition zone determination has been carried out by antagonism assay, as well as diffusion method using Lactobacillus plantarum, Leuconostoc mesenteroides, Staphylococcus aureus, Lactobacillus pentosus and Lactobacillus acidilactici as indicator strains. The results showed that L. plantarum and L. acidilactici were the sensitive indicators. The best growth medium for antagonism assay of the two sensitive indicator bacteria was MRS, which showed inhibition zone diameter of 1.28 cm and 1.23 cm, respectively. The most active supernatant was produced by L. mesenteroides Pbac1 grown on MRS, which inhibited the growth of L. plantarum and L. acidilactici with respective zone diameter of 1.28 cm and 1.19 cm. Bacteriocin titre activity against sensitive indicator bacteria was 100 AU/ml. Based on the result, MRS was further utilized to study the effect of the different carbon sources i.e glucose, maltose and mannose on bacteriocin activity of L. mesenteroides Pbac1. The results showed that glucose was the best carbon source as indicated by the widest diameter of inhibition zone, i.e 1.23 cm, against both indicator strains. Bacteriocin titre activity of the latter study was 100 AU/ml.