The effects of B-site substitution (BMn, Fe, and Co) in La-based perovskite oxides (LPOs); LaMnO3, LaFeO3, LaCoO3, as bifunctional electrocatalysts during oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) in metal-air batteries (MABs) under an alkaline electrolyte (pH = 13) are investigated using density functional theory (DFT). It is found that LaMnO3 exhibits higher ORR activity than others with ORR overpotential (eta ORR) of 0.57 V, but its OER activity is poor with OER overpotential (eta OER) of 1.12 V. The eta ORR (0.59 V) and eta OER (1.13 V) of LaMn0.75Fe0.25O3 closely resemble those of LaMnO3, suggesting that Fe substitution does not yield appreciable enhancements in activity. Fe substitution reduces the ORR and OER activity because the adsorption energies of intermediate species on Fe-substituted LPOs surfaces are too strong to obtain a potential determining step for ORR and OER. According to Sabatier's principle, the LaMn0.25Co0.75O3 demonstrates superior OER activity compared to the other composition, while ORR activity approximates that of LaMnO3, evidenced by eta ORR of 0.65 V and eta OER of 0.53 V. The Co-terminated LaMn0.25Co0.75O3 shows bifunctional activity higher than Mn/Co termination, indicating that Co is an active site for OER and Mn is a promoter for improved ORR activity. The effects of B-site substitution (BMn, Fe, and Co) on La-based perovskite oxides during oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) are investigated via density functional theory. LaMn0.25Co0.75O3 as a promising bifunctional electrocatalyst exhibits ORR/OER overpotentials of 0.65 V/0.53 V due to the presence of Mn and Co promoting electron transfer. image