Impregnation of hypercrosslinked polystyrene (HPS) with tetrahydrofuran (THF) or methanol solutions containing platinic acid resulted in the formation of Pt(II) complexes within the nanocavities of HPS. The highest selectivity (98% at 100% conversion) measured during the catalytic oxidation of L-sorbose in water was obtained with the HPS-Pt-THF complex. The structure of the catalyst isolated after the induction period was analyzed by transmission electron microscopy and X-ray photoelectron spectroscopy. Electron micrographs revealed enlarged Pt nanoclusters, which were most likely responsible for the high catalytic activity and selectivity observed.