Lettuce is the most widely consumed leafy vegetable in the world. Its quality and yield are highly dependent on the growing conditions, including the growing substrate. Peat is commonly used as a growing substrate, but there is a growing interest in finding alternatives to reduce peat usage. One potential alternative is vermicompost, and this study aims to investigate the impact of vermicompost as an additive to peat substrate on the quality and yield of lettuce seedlings. The research was carried out in a greenhouse covered with a polymer film at the Institute of Horticulture and Horticulture of the Lithuanian Agricultural and Forestry Research Center. Lettuce seedlings were grown in peat with varying amounts of vermicompost (0%, 10%, 20%, 30%, 40%, or 50% vermicompost). Various parameters such as lettuce growth, biometric data, the amount of pigments in the leaves, and the accumulation of elements (N, P, K, Ca, and Mg) were evaluated. The addition of vermicompost, regardless of its amount, significantly increased plant height (from 7.5 cm in control up to 10.9 – 11.3 cm with vermicompost), number of leaves (up to 4.2 – 4.6), leaf area (up to 107 – 131 cm²), and the percentage of dry matter accumulation (up to 6.4 – 7.5 %). Vermicompost also had a positive effect on photosynthesis, resulting in higher yields and better quality of lettuce. The summarized research results demonstrate the potential of using vermicompost in the production of high-quality lettuce.