In this study, the inhibition effect of some organic acids as natural antimicrobial agents and also, the efficiency of potassium sorbate which is known and used as a food preservative were researched to compare with each other. Saccharomyces cerevisiae ATCC 9763 and Kluyveromyces lactis ATCC 8585 strains were activated in Malt Ekstract Broth. The inhibitory effects of some concentrations of potassium sorbate (0, 300, 500, 750, 1000 mg L-1) and organic acids which are acetic, lactic and citric acids (0, 0.1, 0.3, 0.5, 0.7, 1.0%) at pH 6.0 was researched. It was determined that the inhibitory effect of K-sorbate and organic acid concentrations are quite different. According to the results of this research, acetic acid concentrations are the most effective and citric acid is the second effective for inhibition of S. cerevisiae, on the other hand, for K. lactis as K-sorbate is the most effective one, acetic acid is the second effective inhibitor. But, lactic acid has the weakest effect for both of yeasts.