Irrigation with saline water is an increasingly pronounced problem that negatively affects the soil-plant system, and hydroponic cultivation can be recommended as a suitable solution. However, the purchase of water-soluble fertilizers represents a large part of the production costs. Therefore, it is necessary to study the possibilities of using seawater at a suitable concentration that does not harm plants that are not halophytes, since untreated sea salt contains numerous minerals. The aim of this work was to determine the chemical composition and yield of swiss chard in a floating hydropon. The two-factorial experiment included 2 solutions: a standard nutrient solution for growing leafy vegetables and seawater, and two swiss chard cultivars ('Charlie' and 'Dark Green Chard') with a sowing density of 38,2 g/m2. During the single harvest of swiss chard yield and nutritional value (dry matter, vitamin C, phenolics, flavonoids, non-flavonoids, chlorophyl, and carotenoids) were determined. The highest dry matter content (13,38%) was found in the leaves of cultivar 'Charlie' grown in saline solution. The use of seawater in the cultivation of 'Dark Green chard' had a negative effect on the dry matter content, i.e. a positive effect on the amount of vitamin C, total phenolics, flavonoids, non-flavonoids, chlorophyll and carotenoids. The cultivar and solution combinations tested in the research resulted in swiss chard yield ranging from 0,93 ('Charlie'×sea solution) to 1,79 kg/m2 ('Dark Green'×standard solution).