The article presents the results of studies on sorption performed on three samples of mortars with similar density of about 2,000 kg/m 3 . The tested mortars differed in their water-to-cement ratio. Three levels of w/c ratio were adopted that were respectively: 0.5; 0.55 and 0.6. The prepared mortars were cut into samples with a thickness of 1 cm, dried to constant weight at a temperature of 105°C and insulated on the side surface with silicone. The experiment was carried out at a temperature of 25°C and at six different levels of relative humidity ϕ ≈ 12, 33, 54, 76, 85, 98%. Relative humidity was provided by saturated solutions of the appropriate salts: LiCl (ϕ ≈ 12%), MgCl 2 (ϕ ≈ 33%), Mg(NO 3 ) 2 (ϕ ≈ 53%), NaCl (ϕ ≈ 76%), KCl (ϕ ≈ 85%), K 2 SO 4 (ϕ ≈ 98%). The adopted level of temperature and range of relative humidity meet the hygrothermal conditions which tend to affect the cement mortar in real life. The long-term measurement results were used to assess the behaviour of the tested mortars under various conditions of moisture and to determine the equilibrium sorptive humidity.