A series of CexZr1-xO2 nanopowders has been prepared via flame spray pyrolysis of metal precursors dissolved in the desired molar ratio in a flammable carrier solvent. This synthetic method relies on the near instantaneous combustion of a fine aerosol mist of the precursor solution followed by rapid thermal quenching which limits both particle growth and phase separation. When 0.5less than or equal toXless than or equal to1, the oxides have the cubic CaF2 structure type with unit cell parameters which decrease as the mole fraction of Ce4+ decreases. Such solid solution behavior continues through 00.1.