Perovskite oxides (POs) are emerging as a class of highly efficient catalysts for reducing oxygen to H₂O. Although a rich variety of POs-based catalysts have been developed by tuning the complex composition, a highly efficient PO catalyst that is able to alter the reaction pathway from a 4e⁻ process to a 2e⁻ process for H₂O₂ production has rarely been achieved. We modified the structure and composition of a Ca- and Nb-based PO material by realizing a uniform two-dimensional (2D) morphology and varied Ta doping, resulting in the 2D Ca₂Nb_3−xTa_xO₁₀⁻ (x = 0, 0.5, 1, and 1.5) monolayer catalysts. The obtained catalysts exhibit a dominant 2e⁻ pathway and show exceptional H₂O₂ production efficiency. The typical Ca₂Nb_2.5Ta_0.5O₁₀⁻ nanoflakes showed an onset potential of 0.735 V vs. reversible hydrogen electrode (RHE), a remarkably high selectivity over 95% across a wide range of 0.3–0.7 V, an impressively high Faradaic efficiency of 94%, and a notable H₂O₂ productivity of 1571 mmol·g_cat⁻¹·h⁻¹. These findings highlight the great potential of 2D perovskite oxide nanoflakes as advanced electrocatalysts for 2e⁻ oxygen reduction reaction.