Lactic acid bacteria (LAB) may be a useful and effective strategy to prevent or reduce the incidence of pathogens, thus improving food safety and consumer health. Kefir is a sour fermented milk and contains a mixture of microorganisms, mainly LAB. The aim was to evaluate the antagonist effect of isolated kefir LAB on indicator LAB kefir strains, assayed by the agar spot test. The kefir LAB isolates (Lactococcus lactis, 4 strains of Leuconostoc mesenteroides, Lactobacillus kefiranofaciens, L. perolens and L. kefiri) were spotted onto the surface of MRS agar plates and incubated at 37ºC for 24 h to allow colonies to develop. The indicator LAB kefir strains (L. casei, 2 strains of L. satsumensis and L. perolens) were inoculated into 15 mL of 0.9% agar MRS and poured over the plate on which the LAB isolates were grown. After incubation at 37ºC for 24-48h, under aerobiosis, the diameters of the inhibition zones around the spots were measured with a caliper. L. mesentoroides and L. perolens showed inhibition zones (4.3 – 7.3mm; 8.7 – 11.7mm, respectively) against all indicator LAB strains. L. lactis, L. kefiranofaciens and L. kefiri did not show antagonism effect. Since some LAB species can be responsible for spoilage in non fermented meat products, these LAB isolates and their antagonist products could be useful for biopreservation. They can be used as part of or adjuncts to starter cultures for fermented foods in order to improve safety and quality.