A study was made of the surface properties of soils sampled from measuring stations SP1 and SP6, located in close proximity of the archaeological site No. 4, Lake Biskupińskie peninsula, in Biskupin. Brunauer-Emmet and Teller (BET) and Polanyi theories were used to analyse the experimental data. The quantities evaluated from experimental data include the specific surface area, S, surface fractal dimension Ds, maximum hygroscopicity, Mh, number of statistical monolayers, and the thickness of sorption layer Vs. The amount of adsorbed water vapour on consecutive samples was quite different. The highest sorption was observed for samples taken from measuring station SP6. Moreover, the sorption increased with the horizon depth. All the isotherms, however, exhibit similar shape and belong to the type II, according to the BET classification. The values of the surface fractal dimension were slightly higher for soils with higher organic matter content than those for soils that were taken from deeper levels and characterized by lower organic matter content. The evaluated values of Ds suggest uniform structure and low porosity of the samples. The highest thickness of the sorbed layer was found for samples with higher content of organic matter, i.e. for the samples from the horizon of 50-90 cm from measuring site SP1 and for samples from measuring site SP6. The obtained values of Mh point out to mineral character of samples taken from measuring site SP1, whereas in the case of the samples from the soils from measuring site SP6 the values of Mh were close to those characteristic for gyttja and for organic soils. All the obtained results suggest that only the soil taken from measuring site SP6 can be treated as a peat soil, while the soil from measuring site SP1 can be treated as a mineral soil.