Carvacrol is a predominant aromatic compound in oil of oregano. It has naturally remarkable antibacterial, antiviral, antifungal and antiparasital effects. In this study, genotoxic and antigenotoxic activities of carvacrol were investigated by the in vitro sister chromatid exchange ( SCE) assay on human peripheral blood lymphocytes. The genotoxicity test was performed with carvacrol in two donors. On the other hand, inhibitory effect of carvacrol was tested in the presence of mitomycin C (MMC) in the same assay. According to data, all doses of carvacrol did not increase the formation of SCE, whereas it inhibited the rate of SCE induced by MMC. In conclusion, carvacrol exhibited a significant antigenotoxic activity in mammalian cells, indicating its potential for use as an antigenotoxic agent.