With ongoing use of preservative chemical compounds in the food industry, in addition to the challenge of microbial resistance, also there is growing concerns over side effects of these compounds. So, the use of herbal essential oils in food preservatives with much less side effects and sometimes even positive effects, has been considered. Therefore, in the present study, the antibacterial effects of Nisin and Satureja montana essential oil have been studied separately and in combination on standard strains of Escherichia coli and Staphylococcus aureus, that are important bacteria in food microbial contamination. Constituents analysis of Satureja essential oil was performed by GC/MS. Antimicrobial susceptibility testing as Minimum Inhibitory Concentration (MIC) and Minimum Bactericidal Concentration (MBC) was performed by Broth micro dilution method and evaluation of interactions between the compounds, was performed by calculating FIC index (Fractional Inhibitory Concentration) method. Antimicrobial susceptibility test showed that MIC and MBC of Satureja montana essential oil and Nisin on S.aureus were 1.25mg/ml and ≤7.8I.U/ml, respectively. and MIC and MBC of Satureja montana and Nisin on E.coli were <10mg/ml and 1000 I.U/ml, respectively. Results of FIC index revealed that antibacterial effects of Satureja montana in combination with Nisin on E.coli O157 , synergistically increased. While, antibacterial effect of the above mentioned compounds on S.aureus was indifferent. Present study showed a significant improvement in the antibacterial effects of Satureja montana essential oil in combination with Nisin on E.coli compared to S.aureus. The effect of Nisin alone on gram-negative bacteria is weak and now faces the challenge of microbial resistance. However, obtaining a stable combination of herbal essential oils containing antimicrobial agents such as Carvacrol for use in food preservation, can be a good point for further research and development.