Saline stress is recognized as one of the most important abiotic stresses for plants in some regions of the world. Recent studies showed that silicon (Si) can play an important role in plant resistance to environmental conditions, such as excessive salinity. In the present experiment, Sinapis nigra L. was exposed to two levels of salinity (50 and 100 mM NaCl). To study the effect of Si addition on the concentrations of K + , Ca 2+ , Na + , and P, in the vegetative parts of plants, 5 mM of Si in the form of fertilizer (Siliplant) was added to the nutrient solutions. The experiment was conducted in semi-controlled conditions. The results showed that both salinity levels significantly increased the concentration of Na + in leaves, stems, and roots, whereas the concentration of Ca 2+ and K + were decreased (up to 55% and 90% in the presence of 100 mM NaCl). The addition of Siliplant to the saline nutrient solution (50 mM NaCl) was efficient in decreasing Na + accumulation in leaves and stem, while in roots more alleviating effect of Si addition was pronounced in the presence of 100 mM NaCl (Na + concentration decreased by 50%). The presence of Si in 50 mM NaCl containing nutrient solution enhanced the accumulation of K + in leaves and stems, while Ca 2+ concentration was decreased, or the addition of Si to a nutrient solution had a negligible effect. Based on the results of the present study, the application of Si in the form of fertilizer was found more efficient in the presence of lower salt concentration (50 mM NaCl). Therefore, higher doses of the fertilizer should be considered and tested in case of higher NaCl concentrations in the substrate.