Nanoparticles with an atomically ordered alloy phase have received enormous attention for application as catalysts in fuel cells because of their unique electronic properties resulting from unusually strong d-orbital interactions between two metal components. However, the synthesis of intermetallic nanoparticles requires a high reaction temperature, thus necessitating the protection of nanoparticles with inorganic layers to prevent aggregation of nanoparticles during synthesis. The protective layer needs to be removed later for application as a catalyst, which is a cumbersome process. Herein, a novel synthetic strategy is reported for the preparation of L10-PtZn intermetallic nanoparticles by utilizing Pt2+-exchanged ZIF-8 nanocubes as a solid-state precursor. The Pt2+-exchanged ZIF-8 phase plays a dual role as a metal ion source for L10-PtZn nanoparticles and as a carbonaceous matrix that restrains the aggregation of nanoparticles during thermal treatment. The L10-PtZn nanoparticles embedded in a hollow carbon nanocage obtained from one-step annealing of Pt2+-exchanged ZIF-8 showed better electrocatalytic activity and durability toward methanol oxidation under acidic electrolyte conditions than those obtained from commercial Pt/C catalysts.