Porous metals attract significant interest for use in diverse electrochemical catalytic applications. However the fabrication of scalable and controlled porous metal structures on the nanoscale, particularly with highly catalytic pure Pt, still remains a significant challenge. We demonstrate highly engineered nanoporous Pt thin films by the dealloying of a Pt-Si binary alloy system with a predetermined alloy composition. Controlled pore dimensions and nanostructures are obtained by tailoring the Pt-Si alloy composition followed by selective Si etching. As a result, isotropic open nanopores are formed in continuous Pt ligaments and the porosity becomes larger on increasing the Si/Pt atomic ratio, which leads to the formation of a higher surface area and active catalytic sites. The formed nanoporous Pt film shows a 32-times-higher catalytic activity than Pt/C catalysts, with a high current density and low charge-transfer resistance during methanol electro-oxidation. The results reported here open up possibilities to develop high-performance and reliable catalytic electrodes in energy and environmental applications.