Abstract The Y_0.4Bi_0.6VO_4 and Y_0.6Bi_0.4VO_4 solid solutions two-phase at x _Bi = 0.95, 0.90, and 0.80 have been formed by the solid-phase synthesis from the initial Y_2O_3, Bi_2O_3, and V_2O_5 oxides burned in air at a temperature of 1173 K for 200 h and their high-temperature heat capacity has been measured in the range of 350–1000 K by differential scanning calorimetry. The thermodynamic properties of the solution solutions have been calculated using the data obtained.