The heat capacities and enthalpy increments of strontium bismuth niobate SrBi2Nb2O9 (SBN) and strontium bismuth tantalate SrBi2Ta2O9 (SBT) were measured by the relaxation method (2–150 K), Calvet-type heat-conduction calorimetry (305–570 K) and drop calorimetry (773–1373 K). The temperature dependences of non-transition heat capacities in the form Cpm = 324.47 + 0.06371T − 5.0755 × 106/T2 J K−1 mol−1 (298–1400 K) and Cpm = 320.22 + 0.06451T − 4.7001 × 106/T2 J K−1 mol−1 (298–1400 K) were derived for SBN and SBT, respectively, by the least-squares method from the experimental data. Furthermore, the standard molar entropies at 298.15 K Sm°(SBN)=327.15±0.80 and Sm°(SBT)=339.23±0.72 J K−1 mol−1 were evaluated from the low-temperature heat capacity measurements.