Hydrogen sulfide (H2S) as a signaling molecule has a great significance in response to biotic and abiotic stress. The aim of the research was to determine the effect of seed priming of sunflower (Helianthus annuus L.) with increasing concentrations of sodium hydrogen sulfide (NaSH) solutions (100, 500, 1000 and 1500 μM), on the indicators of seed vigor and molecular indicators of stress, in seedlings germinated on different solutions of PEG-6000 (H2O; 2.5 %; 5 %; 10 %). In average for all the osmotic stress levels, treatments with NaSH increased germination capacity. At 5 % of PEG, priming with NaSH resulted in increased germination capacity at each concentration of the H2S donors applied. As compared to the water primed or non primed seed, treatments with NaSH increased mass of seedlings. At the highest level of osmotic stress NaSH reduced the level of lipid peroxidation. In seedlings grown from the seed pre treated with NaSH solutions and germinated on water, reduced content of hydrogen peroxide was observed. Content of free proline at 2.5 % PEG, increased with increasing concentrations of NaSH. The results suggest a stimulatory effect of H2S on the germination capacity and seedling weight. The increased accumulation of free proline, decreased lipid peroxidation levels and hydrogen peroxide content, indicating a possible protective role of H2S in seedlings, grown under osmotic stress. The effect of different concentrations of NaSH at certain levels of stress were different, hence further research on the role of H2S under conditions of osmotic stress is needed.