Peat humic acids have been treated at 185°C with 2 M sodium hydroxide solution, both in the presence and in the absence of sodium sulfide. About 6.3% of the material was converted into aliphatic low-molecular—weight carboxylic acids, which were analyzed by capillary gas-liquid chromatography — mass spectrometry. In all, nearly 60 carboxylic acids were identiﬁed, of which glycolic, lactic, 2-hydroxy-2—methylpropanoic, oxalic, malic and 3,4-dide0xyhexaric acids were the main constituents. Minor products included a wide variety of saccharinic acids and related compounds. The nature of the reaction products suggests that they are derived, to large extent, via a peeling-type reaction from carbohydrates or carbohydrate-related structural units of the starting material. The presence of carbohydrate structures as integral parts of peat humic acids is discussed.