The low-temperature heat capacities of mixed oxides in the Bi-Ca-O system have been determined by the relaxation method at temperatures from 15 to about 225 K. The high-temperature heat capacities have been measured from 340 to about 1030 K using differential scanning calorimetry (DSC) in a stepwise mode. From the results, standard molar entropies and molar heat capacities at 298.15 K as well as their temperature dependencies were evaluated.