Developing electrocatalysts with ultrathin nanostructures and high mesoporosity is a relevant high-priority research direction toward enhancing the performance of noble metals. Herein, mesoporous, highly excavated octahedral PtCu 3 nanostructures are prepared by a facile one-pot synthesis. The mesoporous, highly excavated octahedral PtCu 3 nanostructures are built with mutually perpendicular interlaced mesoporous nanosheets with a thickness of ≈4.5 nm. Benefiting from its mesoporous features, three-dimensional (3D) open surfaces, ultrathin nanosheets, and a Cu-rich surface, PtCu 3 exhibits excellent electrocatalytic performance and high antipoisoning activity toward the methanol oxidation reaction. © 2019 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim