The issue of contamination of pistachios with Aspergillus flavus and aflatoxin is a serious and important threatto the production, export and consumption of pistachios worldwide. Investigating the resistance of pistachio cultivars to A. flavus and its relationship with the physicochemical characteristics of pistachio kernels can be considered as one of the main management strategies to deal address aflatoxin contamination. In this research, the resistance of six important pistachio cultivars to A. flavus and aflatoxin was first determined. The relationship between the thickness of the testa (the thin skin on the kernels) and the growth of A. flavus and aflatoxin production was then investigated. The testa of pistachio cultivars was inoculated using a toxin-producing isolate of A. flavus. Eight days after inoculation, the growth and colonization rate of the fungus was measured and evaluated using the Kernel Screening Assay (KSA) method and the amount of aflatoxin determined by the High-Performance Liquid Chromatography (HPLC) method. The thickness of testa was measured using a micrometer. To investigate the possible relationship between the thickness of testa and the growth of A. flavus and aflatoxin production, the correlation coefficient (r) was calculated. According to the results of statistical analysis, the cultivars Shahpasand and Ghaniabadi exhibited the lowest resistance to the growth of A. flavus. The research results indicated that there was no significant relationship between the amount of fungus growth and aflatoxin and the thickness of the pistachio kernel skin in different cultivars.It appears that the chemical characteristics of the pistachio kernel and kernel skin play a more important role in resistance to fungal growth and aflatoxin production. تفاصيل المقالة