In the study presented in the paper water adsorption isotherms were determined for wheat, rye and buckwheat flours at 5, 25 and 40^oC over a range of water activity from 0.112 to 0.945 by static gravimetric method. The water adsorption isotherms had a compatible course with  type II isotherms according to the Brunauer classification. For the description the water adsorption isotherms the GAB model was used which gave good fit to the experimental sorption data. The calculated  root mean square error (RMS) did not exceed 6% and residual coefficient of variation was less than 1%. The process temperature affected the course of adsorption isotherms. Hygroscopicity of the flours increased with lowering of the temperature. The biggest decline of net isosteric heat of water adsorption (q_st,n) in the flours was in the range of water content from 4 to 15 g water (100 g d.m.)^-1. With increase in the amount of adsorbed water above 15 g of water (100 g d.m.)^-1, the net isosteric heat of water adsorption decreased slightly and approached the latent heat of vaporisation for pure water. The highest value of the net isosteric heat of water adsorption at the level of the monolayer was recorded for buckwheat flour (34,7 kJ mol^-1), slightly lower for wheat flour (32,1 kJ mol^-1) and the lowest for rye flour (25,1 kJ mol^-1). Four parameter empirical model correctly described q_st,n  changes in the function of water content in tested flours. The calculated RMS value did not exceed 34% and V_e value was less than 9%.