Antimicrobial activity of a commercial olive leaf extract (OLE) against Bacillus cereus, Listeria monocytogenes, Staphylococcus aureus, Escherichia coli O157:H7, Escherichia coli Biotype I, Salmonella Enteritidis and Salmonella Typhimurium was tested by disc diffusion assay. The Gram negative bacteria tested in this study were more sensitive to OLE than Gram negatives. The highest antimicrobial activity was on L. monocytogenes which yielded the largest inhibitions zone. Effect of OLE on thermal resistance of L. monocytogenes was tested both in Tryptic Soy Broth supplemented with 0.6% yeast extract (TSBYE) and sous vide packed ground beef. OLE added TSBYE (0, 0.5, 1%) tubes and ground beef (0, 1%) samples were inoculated with L. monocytogenes (7-8 log cfu/ml-g) and heated at 55, 60 and 65°C up to 30, 20 and 7.5 minutes, respectively. Total reductions in TSBYE tubes added with 0.5 and 1% OLE were slightly higher than control tubes (0% OLE) for all temperatures. Counts of L. monocytogenes in sous vide packed ground beef samples added with 1% OLE and then cooked at 55°C (30 min), 60°C (20 min) and 65°C (7.5 min) were 0.31, 1.04 and 0.73 log cfu/g lower than those control samples, respectively. The results indicate that OLE included in formulation may be an additional hurdle to control L. monocytogenes in heat processed ground beef.