The dissertation is based on research on the optimization of the biofortification model of spinach (Spinacia oleracea L.) and arugula (Eruca sativa Mill.) with selenium - a conventional approach with the use of selenate and a nanobiotechnological approach with the use of selenium nanoparticles. The aim of this research was to optimize the production of leafy vegetables in a floating hydroponic system, to select the optimal biofortification model depending on the form and concentration of selenium for several types of leafy vegetables in order to meet the recommended daily intake of selenium in the human body, and to determine the effect of the applied biofortification models on growth and development, mineral composition and antioxidant properties of the tested species. The research was conducted in a heated greenhouse with automatic temperature and ventilation control in a floating hydroponic system during 2019 and 2020. Statistical processing of the data revealed that biofortification with different forms of Se significantly affects the number of leaves, root length and fresh and dry weight in both tested species. Biofortification with different forms of Se also influenced changes in the content of macro and microelements in the examined species. In the case of Se content, a linear trend of increasing Se content in the roots and leaves of the examined species was determined in all biofortification treatments. A significantly higher Se content was found in the roots of spinach and arugula with SeNPs treatment. On the contrary, the significantly highest content of Se in spinach and rocket leaves was found in the treatment with selenate. Biofortification treatments increased the concentrations of chlorophyll a (Chl a), chlorophyll b (Chl b) and carotenoids (Car) in both tested species. Also, biofortification with different forms of Se significantly influenced both enzymatic and non-enzymatic indicators of oxidative stress depending on the plant species and the form and concentration of selenium. Selenium biofortification increased the concentration of total phenols (PHE), glutation (GSH) and ascorbic acid (AA) in the examined species, which was reflected in the increase of total antioxidant activity (UAA). In general, biofortification treatments had a significant effect on the reduction of lipid peroxidation (LPO) levels in both tested species. Also, the effect of increasing the activity of the enzymes ascorbate peroxidase (APX), catalase (CAT), superoxide dismutase (SOD), glutathione reductase (GR) and glutathione S-transferase (GST) during the biofortification treatment among the examined species was determined, while the effect on increasing the activity of the enzyme glutathione peroxidase (GPX) was absent.