This study conducted the CO₂ methanation reaction over the nickel-based catalysts supported on CaO.Al₂O₃ with different CaO/Al₂O₃ molar ratios. The catalyst support was synthesized with the mechanochemical method, and the influence of nickel loading was investigated on the selected catalyst support with an appropriate CaO/Al₂O₃ molar ratio. According to the results, incorporating Al₂O₃ into the CaO increased the BET area from 5 to 196 m² g⁻¹. Also, the S_BET of the calcined catalysts decreased with the augmentation of nickel oxide percentage from 5 to 15 wt% due to the pore blocking of the support after metal addition. Moreover, the activity of catalysts enhanced with the increment of CaO/Al₂O₃ molar ratio and NiO percentage, ascribed to the improvement in the reducibility of the catalysts. However, the excessive addition of CaO and nickel oxide reduced the CO₂ conversion because of a significant decrease in surface area. Therefore, 10 wt% NiO/CaO.2Al₂O₃ catalyst possessed superior CO₂ conversion (79.1%) and CH₄ selectivity (98.1%) in CO₂ methanation reaction at 450 °C, H₂/CO₂ = 4 and GHSV = 18,000 ml h⁻¹.g⁻¹_cat. The selected sample illustrated great stability for 11 h without any remarkable change in its initial catalytic activity. The impact of GHSV on the catalytic performance of the selected catalyst was evaluated, and the outcomes exhibited that decrement in GHSV value enhanced CO₂ conversion. With the increment of feed ratio (H₂/CO₂) from 2 to 5, CO₂ conversion reached 93.3%, ascribed to the existence of adequate hydrogen to react with CO₂.