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The paper presents the results of lysometric studies of the composition of organic matter of peat soils depending on the level of groundwater occurrence. It is established that the amount of bitumen in the arable layer (0.2 m) of medium-power peat soil at 0.5 m ground water level (UGV) is less by 1.65 % than at the depth of 1.0 m and by 4.34 % at 1.5 m. There is no specific dependence on the UHW downstream of the soil profile. The increase of groundwater depth from 0.5 to 1.5 m reduces the amount of water-soluble and easily hydrolyzed substances in the arable layer at 100 °C from 5.68 to 4.48 %. At the groundwater level of 0.5 m, the maximum presence (34.25 %) of substances hydrolysable by 2 % HCl was determined, which is 3.4–3.8 % higher than at 1–1.5 m. The maximum amount of humic acids in peat soil (32.05 %) is set at 0.5 m CKD. In the arable layer, the excess is 4.5 % in comparison with one and a half meters of groundwater. The amount of fulvic acids practically does not depend on the groundwater table and is within the range of 17.7–17.9 %. With the same botanical composition of peat, the increase in the depth of groundwater occurrence from 0.5 to 1.5 m reduces the content of hard-tohydrolyze 80 % of H2SO4 substances in the arable layer from 2.82 to 2.31 %. The number of compounds difficult to hydrolyze with acid is represented by 46–52 % cellulose and does not depend on the level of groundwater. The presence of lignin in peat is several times higher than the cellulose content. There is a dependence of decrease in the lignin content at increase in depth of occurrence of ground waters from 0.5 m (6.63 %) to 1.5 m (5.23 %).