Juglans regia walnut shell is a rich source of phenolic compounds, of which the tannins manifesting high antioxidant, antibacterial and anticandidic activity [1]. The aim of the present research was to establish the antimicrobial activity of the intact and oxidized tannins isolated from the walnut septum J. regia. J. regia walnut septum served as a vegetable raw material for the obtaining of the tannins. The testing of the antimicrobial activity of the tannins was performed on the bacteria Bacillus subtilis - gram-positive, Pseudomonas fluorescens¸ Erwinia amylovora, E. carotovora, Xanthomonas campestris - gram-negative, the yeast Candida utilis, the fungi Fusarium. The extraction and oxidation of the tannins were performed by static method (maceration, periodic draining), taking into account also important factors, such as the concentration of the solvent, the ratio of plant product: solvent, extraction duration. The total content of the polyphenolic compounds was determined by spectrophotometric method with Folin-Ciocalteu color reagent [2]. The following were established: 1) intact and oxidized tannin extracts, show differentiated antibacterial and antifungal action depending on the concentration of the preparation and the species of the microorganisms; 2) the oxidation of the tannin extract led to the increase of the antibacterial activity for E. amylovora and E. carotovora, and its decrease for B. subtilis, the efficient concentrations being 0.15; 0.15 and 0.3%, respectively; 3) the highest antifungal activity presented the intact and oxidized tannins in the concentration of 0.05% for D. sorokiniana, followed by the oxidized tannins-0.05% for F. oxysporum; 4) the tannin extracts determined the development of small spores and the inhibition of the intracellular wall biosynthesis (D. sorokinana), premature germination of spores and an uneven development of fungal mycelium hyphae (F. oxysporum).