Two-step water splitting reaction with the reactive ceramics of cerium dioxide (CeO₂) and zirconium dioxide (ZrO₂) solid solutions (Ce-Zr system) which can be applied for solar hydrogen production using concentrated solar thermal energy has been studied. These reactive ceramics are high-temperature resistance and high ion conductivity and the reaction proceeds at high temperature (>1773K) and the high-flux energy (1000-3000 kW/m²) is sufficiently absorbed. The samples of Ce-Zr system were prepared by oxalate coprecipitation method (The molar ratio of Ce : Zr were adjusted 100 : 0, 80 : 20 and 60 : 40.) and by polymerized complex method (Ce : Zr was adjusted 60 : 40). These samples prepared by oxalate coprecipitation method were cubic-main system and the sample prepared by polymerized complex method was tetragonal system. No H₂-generation reaction proceeds with tetragonal system at 673-873K, but with cubic-main system, indicating that the reactivity of the two-step water splitting reaction with Ce-Zr system chemical composition of Ce60Zr40 is difficult depending on the crystal system. The reactivity of the two-step water splitting process is enhanced and the O₂-releasing temperature is lowered by doping ZrO₂ in CeO₂. The amounts of H₂ evolved in the H₂-generation reaction with Ce60Zr40 (cubic-main system prepared by oxalate coprecipitation method) is less than those of Ce100 and Ce80Zr20 at 1473-1573K, but more than those at 1773K. The reaction mechanism on the difference of those H₂-generation reactions was investigated.