The heat capacity and the enthalpy increments of strontium niobate Sr2Nb2O7 and calcium niobate Ca2Nb2O7 were measured by the relaxation time method (2-300K), DSC (260-360K) and drop calorimetry (720-1370K). Temperature dependencies of the molar heat capacity in the form C-pm = 248.0 + 0.04350T - 3.948 x 10(6)/T-2 JK(-1) for Sr2Nb2O7 and C-pm = 257.2 + 0.03621T - 4.434 x 10(6)/T-2 J K-1 mol(-1) for Ca2Nb2O7 were derived by the least-square method from the experimental data. The molar entropies at 298.15 K, S-m degrees (298.15 K) = 238.5 +/- 1.3 JK(-1) mol(-1) for Sr2Nb2O7 and S-m degrees(298.15 K) = 212.4 +/- 1.2 JK(-1) mol(-1) for Ca2Nb2O7, were evaluated from the low-temperature heat capacity measurements. (C) 2008 Elsevier B.V. All rights reserved.