Tea (Camellia sinensis L.) is one of the ancestral cultures cultivated by man, currently spread in about 50 countries on all continents, tea consumption being a favorite drink throughout the world. Research has shown antibacterial and antifungal activity of tea extracts [1, 2]. The purpose of the research was to elucidate the antimicrobial activities of intact and oxidized tannins isolated from commercial green and black tea leaves. Antimicrobial tannin activity was tested on Bacillus, Pseudomonas, Erwinia, Xantomonas, and Alternaria and Fusarium filamentous fungi. The bacteria B. subtilis, Ps. fluorescens, E. amylovora, E. carotovora, X. campestris were cultured on peptone agar, supplemented with tannins at concentrations of 1.25; 0.6; 0.3; 0.15; 0.07; 0.035; 0.0017; 0.0085; 0.004%. The bacterial concentration of 4.8 x 10⁸ UFC / ml used in research is the bacterial turbidity of 2.0 according to McFarland index. Screening of antifungal activity of tannins was performed by supplementing them at concentrations of 0.002; 0.01; 0.05; 0.25% on PDA nutritional medium (potato dextrosis agar). Intact tannin extracts from green tea showed antibacterial activity (B. subtilis, P. fluorescens, E. amylovora, E. carotovora, X. campestris) in the concentration range 0.07 ... 0.25% and oxidized – 0.017 ... 1.25%, which indicates that the increase of the total content of functional groups (carboxyl and phenolic) in the process of oxidation of extracts leads to increased antibacterial activity. Thus, the oxidation of green tea tannin extracts contributed to the significant increase in the antifungal activity (A. alternata, F. oxysporum, F. solani), manifested by the inhibition of colony growth and the decrease of mycelial density, especially in the concentration of 0.25%. Black tea tannin extracts showed antibacterial properties in the concentration range of 0.035% -0.07% and anticandidal at the concentration of 0.017%. The strongest suppressive effect for D. sorokiniana was confirmed at a concentration of 0.05%, the diameter of the colony being 13.6-20.0% lower than in the control variant. In all of the studied variants the mycelial density was 3-3.5 times lower than in the control variant. Also, under the influence of these extracts there was a significant discoloring of the mycelium, which denotes the strong capacities of pigmentogenesis inhibition, which leads to a decrease in the adaptability and pathogenic potential of the fungi.