The antimicrobial activity of 10 substances with antimicrobial activity used as food preservatives and antioxidants was evaluated by the Impedance Splitting (IS) method and the Agar Dilution Method on five microorganisms (Escherichia coli (ATCC 10536), Staphylococcus aureus (ATCC 6538), Ps. aeruginosa (ATCC 9027), Candida albicans (ATCC 10231) and Aspergillus niger (ATCC 6275)). In both methods the Maximum Inhibitory Dilution (MID) of the preservatives was determined. MID was equal in 68% of cases and different by one dilution cycle in 32% of cases. The results suggest that the IS method, which is more automated and less laborious, could be used as an alternative method for the estimation of the antimicrobial activity of food antimicrobial substances.