Ultrathin Pt nanostructures exposing controlled crystal facets are highly desirable for their superior activity and cost-effectiveness in the electrocatalytic oxygen reduction reaction (ORR), and they are conventionally synthesized by epitaxial growth of Pt on a limited range of templates, such as Pd nanocrystals, resulting in a high cost and less structural diversity of the ultrathin Pt nanostructures. To solve this problem, we demonstrate that ultrathin Pt nanostructures can be synthesized by templating conveniently available Ag nanocrystals without involving galvanic replacement, which enables a much-reduced cost and controllable new morphologies, such as ultrathin Pt nanoplates that expose the {111} facets. The resulting ultrathin Pt nanoplates are ∼1-2 nm in thickness, which show an ∼22-fold increase in specific activity (5.3 mA cm-2), an ∼9.5-fold increase in mass activity (1.62 A mg-1) and significantly enhanced catalytic stability in the ORR, compared with the commercial Pt/C catalyst. We believe this strategy opens a door to a highly extendable family of ultrathin noble metal nanostructures, thus promising excellent activity and stability in a broad range of catalytic applications.