Solid solutions of dawsonites, ammonium aluminum carbonate hydroxide-ammonium gallium carbonate hydroxide, were obtained by the addition of aqueous solutions of mixtures of aluminum and gallium nitrates to an excess ammonium carbonate solution. The dawsonite solid solutions were calcined at 700 degrees C to give gamma-Ga2O3-Al2O3 solid solutions. The structures of these two types of solid solution were discussed on the basis of their X-ray diffraction patterns and X-ray absorption fine structure spectra.