Rationally designing active and durable catalysts for the oxygen evolution reaction (OER) is of primary importance in water splitting. Perovskite oxides (ABO3) with versatile structures and multiple physicochemical properties have triggered considerable interest in the OER. The leaching of A site cations can create nanostructures and amorphous motifs on the perovskite matrix, thus facilitating the OER process. However, selectively dissolving A site cations and simultaneously obtaining more active amorphous motifs derived from the B site cations remains a great challenge. Herein, a top-down strategy is proposed to transform bulk crystalline perovskite (LaNiO3) into a nanostructured amorphous hydroxide by FeCl3 post-treatment, resulting in an extremely low overpotential of 189 mV at 10 mA cm−2. The top-down-constructed amorphous catalyst with a large surface area has dual NiFe active sites, where high-valence Ni3+-based edge-sharing octahedral frameworks are surrounded by interstitial distorted Fe octahedra and contribute to the superior OER performance. This top-down strategy provides a valid way to design novel perovskite-derived catalysts.