Mycotoxin contamination in foods and feeds poses serious health hazard to humans and animals. Aflatoxins, which are mutagenic, carcinogenic, teratogenic, hepatotoxic and immunosuppressive, could be produced by certain strains of Aspergillus parasiticus, A. nominus and A. flavus. An aim of this study was to examine the antifungal activity of various essential oils(EOs) obtained fromM. longifolia, Nepeta asterotricha, Ziziphora clinopodioides, Ferula assa- foetida and Heracleum persicum against A. flavus. Comparing the effect of EOs obtained from five plant species mentioned above showed that at 2000 ppm concentration all EOs tested were capable of inhibiting mycelia growth of A. flavus ranging from 100% to 18%. The highest and lowest levels of antifungal effect were obtained using M. longifolia and Heracleum persicum, respectively.Gas chromatography (GC) and GC-mass spectrometry analyses were applied to determine the constituents of M. Longifolia oil, as the most effective EO in suppressing A. flavus growth. Obtained data indicated that the main compounds of this EO were limonene (1.7%), 1,8-cineole (2.2%), 1-borneol (1%), isopiperitenone (1.3%), piperitenone (18.7%) and piperitenone oxide (70%). Spore germination of A. flavus was completely inhibited by IC50 and MIC concentrations of M. longifolia EO. Whereas, these concentrations of the EO had no inhibitory effect on sporulation of the fungus. Morphological changes of A. flavus via application of M. longifolia EO at IC50 concentration were compared with control and considerable alterations in the hyphae and conidiophores of treated samples were observed. Aflatoxin production by A. flavus significantly decreased at MIC concentration of M. longifolia EO compared to control. Only aflatoxin B1 was detected at low concentration using the MIC level of this EO. So, the EO obtained from M. longifolia might be used as a biological agent to decrease mycelial growth and aflatoxin production of A. flavus for protecting crops from this toxigenic fungus

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