Essential oils are aromatic liquidsfrom plant material that possess more or less pronounced antimicrobial activity. Due to the increasing need for producing food without synthetic additives, the addition of essential oils as antimicrobial and antifugal additives represent a great potential in producing microbiologically safe foods. The task was to examine the antifungal activity of essential oil of thyme and tea tree oil on selected species of Aspergillus carbonarius, A. flavus and A. parasiticus. We examined the minimum inhibitory (MIC) and minimal fungicidal concentrations (MFK) of essential oils and the effect of essential oils in the inhibition of linear growth of mold colonies at different values of water activity (aw). Fungicidal effect of tea tree oil in all tested species of mold showed the same concentration of 20 000 ppm. Similar fungicidal effect of essential oil of thyme is observed on tested species of the genus Aspergillus, with the exception of A. carbonarius, which proved to be the most sensitive species of this genus of mold due to the fungicidal concentration of 10 000 ppm. Comparing macrobroth and semisolid method, the latter proved to be more proper since both essential oil showed greater antifungal properties at lower concentrations. During monitoring of linear growth of mold colonies in aw0.95 and 0. 98, supplement of essential tea tree oil had no fungicidal effect but there was extension in lag phase of growth, depending on the concentration. The addition of the highest concentration of thyme essential oil in A. carbonarius growth medium had fungicidal effect. Both essential oils had inhibitory effect while testing linear growth of A. flavus and A. parasiticus at aw values 0.95 and 0.98.