A study was carried out on the fungal contamination of commercially available hazelnuts, and the effect of different factors (water activity, temperature and presence of potassium sorbate) on fungal growth and aflatoxin production in hazelnuts. All samples (100%) of raw hazelnuts showed fungal contamination. None of the samples showed aflatoxin contamination, but when hazelnuts were inoculated with Aspergillus parasiticus, and water activity and temperature were optimal formold growth, high production of aflatoxin was found. Potassium sorbate at subinhibitory levels seemed to inhibit fungal growth, but enhanced aflatoxin production.