The results of isotopic investigations of the Skaliska Basin sediments are presented. Stable isotope analyses were done for authigenic carbonates from three profi les: W1 – Piotrowo-Ławniki, W2 – Sąkieły Małe, and W4 – Budzewo. The profi les contain carbonate silts at the bottom, then calcareous detritus gyttja and organic silts and peat at the top. Palynological data indicate that sediment were accumulated in the Skaliska Basin from the fi nal phase of the Younger Dryas to the Subboreal period. The values δ18O change from ca −9.4 to −4.5‰, and δ13C values varies from −5.1 to +0.1‰. Such a large range of isotopic data refl ects changing conditions in the basin during accumulation of deposits (different water levels, water temperatures, and bioproduction). Based on the results of stable isotope analyses of the carbonates, isotopic zones (Is) were defi ned and characterized for each profi le. The results of isotopic analysis enabled reconstruction of varying environmental conditions connected with lake deepening and/or infl ux of water enriched in light isotopes, climatic warming, and increase of biological activity. The Late Glacial deposits are characterized by δ18O values of ca −6.5–6‰ and δ13C of ca −1‰. In the transitional time between the Late Glacial and the Holocene, δ18O systematically falls below −8‰, refl ecting a substantial change in the isotopic composition of the lake water, likely caused by to infl ow of melt water. During the Preboreal period the δ18O as well as the δ13C values systematically decrease and reach minima (−8.4–9.4‰ for δ18O and ca −3.5–4.7‰ for δ13C). At the beginning of the Boreal period, an increase of ca 2‰ in δ18O is noted and is associated with climatic warming. During the Atlantic period the varying trends in the δ18O record are likely connected with changing precipitation/evaporation ratios, causing changes in the isotope composition of the water. The fl uctuations of the isotopic values in the upper parts of the successions probably point to shallowing of the lake due to sedimentary infi ll.