The aim of this study was to evaluate the sorption properties of bakery raw materials for baking bread. The research material was designated in the study as A, B, C, D, where A – is a whole-grain rye flour type 2000, B – whole spelt wheat flour; C – mix of flours A and B (75A:25B) and D – crumb of fresh mixed rye-spelt bread (75A:25B) - independently prepared at home. Sorption properties were tested by assigning static sorption isotherms of water activity a_w = 0.07-0.979. The samples were stored at 20±1ºC for 45 days. Isotherms were mathematical description of the sample using the BET equation, using the Curie Table 2 D v3. Based on the equilibrium moisture content of the products the capacity of BET adsorption monolayers surface area and sorption were determined. The plotted isotherms exhibited sigmoid shapes of curves characteristic for isotherms of II type, with deviations dependent on the nature of the sorption-adsorption process, in the raw materials A, B and C and the desorption of crumb of fresh mixed rye-spelt bread D. The results showed that the highest capacity of monolayer (Vm) was characterized by a rye flour and the water filling the monolayer was characterized by the highest activity (a_w = 0.196) compared with the studied materials, B and C.