Thermodynamic properties of sodium borosilicate glasses {56.7 SiO2- (43.7-x) B2O3, xNa(2)O} where x = 14.4, 22.9, and 32.5, have been studied. The heat capacity was measured using an adiabatic calorimeter at temperatures between 13 K and 300 K. The thermodynamic functions were calculated from the smoothed values of C-p,C-m. The results differ from an additive model with pure glassy SiO2, B2O3, and crystalline Na2O as components. A model based on the assumption that the contribution of structural units of glasses to the heat capacity is equal to those of glasses with the same molecular formula is proposed.