Selenium is a chemical element essential for the health of living organisms. In the form of nanoparticles, selenium shows greater biological effectiveness and smaller toxicity than inorganic selenite, then also equal biological effectiveness, but reduced toxicity than selenomethionine. The objective of this graduate thesis was to use the extracts obtained from the pomace of tangerines, tomatoes and olives in biogenic synthesis of selenium nanoparticles. For the purpose of this thesis, synthetised selenium nanoparticles were stabilized using crude and purified pectins obtained from the pomace of tangerines and tomatoes, while in one half of the samples olive pomace extract was added in order to study the possibilities of additional functionalisation of the synthetised nanosystems in terms of improvement of antioxidative activity. The obtained samples were characterized through determining particle size distribution, concentration and zeta potential (DLS method), then through determining reductive and antiradical ability (TEAC and FC method). Also, nanosystem stability was analysed by repeating the measurements of particle size, concentration and zeta potential after 2, 5, 9, 20 and 30 days from the beginning of the analysis. The samples stabilized by tomato pomace pectins showed smaller particle size values and more negative zeta potential in relation to the samples stabilized by tangerine pomace pectins. The samples functionalized with the addition of olive pomace extract showed significantly greater values of antioxidative potential (using both applied methods) which indicates that olive pomace extract is a powerful natural antioxidant applicable in the biogenic synthesis of selenium nanoparticles. Future research activities should study the possibilities for synthetising selenium nanoparticles inferior to 100 nm, which would potentially show better biological effects and greater stability, but also explore bioavailability and other aspects of biological effects of the resulting nanosystems.