The structure of mycobiota (epiphytic and from inner tissues) of Q. robur acorns (580 samples) under conditions of Kyiv Polissya was studied. Acorn samples were collected from oak trees during vegetation period. The epiphytes and mycobiota isolated from inner tissues of acorns was represented by 38 and 20 species, respectively. The majority of fungi were isolated in July. Cosmopolitan and non-specific species Acremonium sp., Alternaria alternata, Cladosporium cladosporioides, Trichoderma harzianum, T. viride and specific ones - Phoma sp. and Phomopsis sp. were isolated from inner acorn tissues. It was established that potential seed and seedling pathogens infect acorns during the process of their formation. The paper is presented in Ukrainian.