The present research aims at evaluating the effect of silicon on the photosynthetic rate and the chlorophyll fluorescence parameters of hydroponically grown young cucumber plants (Cucumis sativus L.), cv. Gergana, under salinity stress. The experiment was conducted in a climatic chamber at the Department of Plant Physiology and Biochemistry, Agricultural University – Plovdiv. Four variants were examined: 1 – control, 2 – NaCl, 3 – Si, and 4 – NaCl + Si. Plants were grown in a nutrient solution and were treated with 50 mM NaCl and 1.5 mM Si in form of Na2SiO3. The results showed a decrease in the photosynthetic rate by 25% for the NaCl variant compared to the control. Silicon supply increased the photosynthetic rate of the salt-stressed plants by 17%. Salinity had also a negative effect on of the chlorophyll fluorescence parameters and the content of photosynthetic pigments, which were dramatically reduced. It was established that the silicon supply had a positive influence on the photosynthetic rate, the chlorophyll fluorescence parameters and the pigment content of the treated cucumber plants. The content of chlorophyll a, chlorophyll b, total chlorophyll, and carotenoids increased.