Selenium (Se) is an essential microelement for a human having antioxidant and anticancerous properties. One of the ways to increase its concentration in plants is biofortification through various agronomic practices including artificial lighting. The aim of the study was to determine the responses of baby leaf lettuce to various Se content in hydroponic solution at different ratio of blue (B) and red (R) light of light-emitting diodes (LED) lighting Lettuce (Lactuca sativa, ‘Little Gem’) were grown hydroponically under B: R light ratios - 10B:90R%, 75B:25R% 21 days after sowing (DAS). The photon flux density (PFD), photoperiod, temperature, and relative humidity in the growth chamber were maintained at 220 mol m^-2 s-¹, 18 h, 21/17±2^oC, and 60±5%, respectively. Two experiments with Se were performed using natrium selenate (Na₂SeO₄). Results of the first experiment (Se - 0, 1, 3 ppm) showed that the content of Se in lettuce was about 15 times higher at 3 ppm compared to 1 ppm. Similar trends were observed for both B and R ratios. However, even the lowest dose of Se inhibited lettuce growth and reduced chlorophyll content. Therefore, a second experiment was performed with lower Se doses (0, 0.5, 1 ppm) at different growth stages (11^th and 17^thDAS). It was found that when Se exposure was initiated at 17^th DAS, lettuce accumulated lower Se content compared to 11^th DAS, but this did not have a negative effect on their growth. B:R ratios 10B:90R% resulted in higher Se content in the leaves. Overall, these results suggest that properly composed doses of Se and LED lighting could be a suitable way for the cultivation of selenium-biofortified baby leaf lettuces without any adverse effects on growth. Acknowledgements: This project has received funding from the Research Council of Lithuania (LMTLT), agreement No. S-MIP-19-2.