High-performance thermochemical water splitting catalyst is the key in solar-driven H₂ production for the development of sustainable and clean energy technology. Perovskite oxides have been considered promising redox catalysts for two-step thermochemical H₂O splitting cycles due to their remarkable oxygen exchange capacity at low thermal heating temperatures. This study is the first to investigate perovskite series of La₁₋ₓCa ₓ CoO₃ for two-step thermochemical H₂O splitting cycles. The Ca doping contents in La₁₋ₓCa ₓ CoO₃ perovskites showed a significant effect on the O₂ and H₂ production performances. Increasing the Ca doping content has greatly increased O₂ evolution during the thermal reduction process. However, high Ca dopant content significantly weakened the reaction thermodynamics of the subsequent H₂O splitting and led to lower re-oxidation yields. After tuning the Ca doping level from 0.2 to 0.8, La₀.₆Ca₀.₄CoO₃ was identified as the best trade-off among the tested La₁₋ₓCa ₓ CoO₃ perovskites. The thermal reduction and water splitting temperatures were also systematically investigated to optimize the thermochemical operational conditions. La₀.₆Ca₀.₄CoO₃ showed maximum H₂ production of 587 µmol g⁻¹ when the two-step thermochemical H₂O splitting carried out between 1300 and 900 °C, eighteen times higher than that of CeO₂ under the same experimental condition. More importantly, La₀.₆Ca₀.₄CoO₃ also exhibited fairly good catalytic stability during the thermochemical cycling test and has strong potential for long-term applications.