Methods: In this study, Concentrations of 50, 100, 200, 300, 500, 1000 and 2000 µg/ml of four essential oils, Eugenia caryophyllata (Clove), Cinnamum zeylanicum (Cinnamon), Thymus vulgaris (Thyme) and Zataria multiflora, were tested in Salmonella typhymurium strains TA100 with and without rat liver S9 using Ames Salmonella reversion assay. Results: Without S9 fraction, increase in mutant colonies per plate was not observed in all used concentrations. Also with S9 fraction all of samples had no significant increase in mutant colonies per plate except Clove in 500 µg/ml, and higher concentrations. Conclusion: Based on obtained results, Clove oil may have mutagenic effect in 500 µg/ml and higher concentration.