Platinum nanoparticle catalysts are essential for achieving energy-efficient and greener chemical processes that involve breaking or establishing of H-H, C-H, or O-H bonds. In this work, we report an innovative top-down strategy to prepare the supported Pt nanoparticles with an average size of approximately 2 nm, starting directly from bulk metallic Pt by metallurgical method. Bulk platinum was dissolved in liquid lithium and ruptured into nanoparticles. This Li-Pt liquid alloy was quenched into Li-Pt solid solution. The lithium content was further converted into LiOH. The resulting powder of Pt nanoparticles in LiOH can be mixed with any nonaqueous support materials. Thereafter, the LiOH can be selectively leached off by water, allowing Pt nanoparticles to be adsorbed on the desired support material. Transmission electron microscope and extended X-ray absorption fine structure analyses demonstrated that the as-formed Pt nanoparticles have an average size of around 2 nm. The carbon-supported Pt nanoparticles prepared by this method inherit more characteristics of their bulk counterparts so that high specific catalytic activity of bulk Pt is maintained, which is confirmed by a preliminary electrocatalytic characterization of oxygen reduction reaction (ORR).