Several mixed perovskites of the type A(2)B'B"O-6 (AB(1/2)'B-1/2"O-3), where A is Ba+2 and B' and B" are trivalent and pentavalent ions, respectively, were synthesized by calcining requisite mixtures of BaCO3, B-2'O-3, and B-2"O-5 in air. X-ray diffraction confirmed the formation of the perovskite phase in each of the samples synthesized. The as-calcined powders were boiled in water to examine their stabilities in water. All mixed perovskites were found. to be stable. By contrast, BaCeO3 and BaPrO3 decomposed when boiled in water while BaZrO3 was found to be stable. Madelung energies of simple and mixed perovskites were computed. The higher stability of mixed perovskites compared to simple perovskites of the type ABO(3), such as BaCeO3 and BaPrO3, where B is a tetravalent ion, was rationalized on the basis of lower Madelung energies of mixed perovskites.