Carvacrol was found in essential oils of thyme, oregano, wild bergamot, and some other plants. Although, a wide range of bioactivities such as anticancer, antioxidant, and antimicrobial has been identified for carvacrol, however, among all therapeutic properties it possesses a potent antimicrobial activity. The present study investigates the inhibitory effect of carvacrol as an active compound against the growth of Aspergillus flavus, besides its effect on the expression of aflatoxin-related (aflR) gene. Twelve fungal samples of A. flavus were used and the antimicrobial activity of carvacrol was tested against them using the minimum inhibitory concentration (MIC) and minimal fungicidal concentration (MFC) according to the broth microdilution procedure. The expression of the aflatoxin regulatory (aflR) gene was examined by Reverse Transcriptase polymerase chain reaction (RT-PCR) technique. The results of MIC and MFC tests showed that carvacrol at 0.8 μg/ml and 3.5 μg/ml concentrations displayed antimicrobial activities on A. flavus, respectively. The RT-PCR result indicated that the expression level of aflR gene had decreased to 33% in the presence of carvacrol compared to 67% in the absence of the mentioned active compound. Together the results demonstrated that carvacrol not only exhibited antimicrobial activity against A. flavus but also reduced its gene expression level. تفاصيل المقالة