It was established that at 298 K the molar heat capacity of alkali metal silicates K2O· nSiO2, Rb2O· nSiO2 and Cs2O· nSiO2 changes linearly when changing n from 1 to 4. Based on the dependencies Cop,298=f(n), the values of the heat capacities K2O, Rb2O and Cs2O have been specified. Keywords: heat capacity, oxides and silicates of alkali metals.