Solid acid catalysts composed of sulfated binary metal oxides, SO42–/TiO2–ZrO2, SO42–/Fe2O3–Al2O3, SO42–/ZrO2–Al2O3, and SO42–/Al2O3–ZrO2 were prepared via a solid-liquid interface reaction of the corresponding hydrated metal sulfates with a metal alkoxide. Sulfated SnO2–TiO2 was prepared via the interface reaction of tin(IV) oxyhydroxide containing nonstoichiometric water molecules with titanium alkoxide. The sulfated binary oxides exhibited greater activity than proton-type zeolites and sulfated zirconia for acid-catalyzed ethanol dehydration. The activation temperatures that provided the highest activity were the same or higher than those for sulfated simple metal oxides. The Al2O3 included in the prepared binary oxides was amorphous even when the heat treatment was conducted at higher temperatures. An increase in thermal stability was observed for anatase–phase TiO2 and tetragonal-phase ZrO2. A well-mixed solid solution was formed by the reaction of Ti(OCH(CH3)2)4 with SnO(OH)2 containing nonstoichiometric water molecules. The SO42–/SnO2–TiO2 showed extremely higher activity in the tested catalysts.