This communication discusses the formation of thin films of platinum colloidal particles by organization at the air-water interface. The platinum clusters were prepared by sodium borohydride reduction of aqueous chloroplatinic acid with the nanoparticles being capped with a polymer, poly(vinylpyrrolidone) (PVP). After separation from the aqueous medium, the capped clusters were dispersed on the surface of water, using the hydrophobic component of the capping agent to organize the clusters at the air-water interface. Pressure-area measurements showed a region of rather low compressibility, characteristic of a reasonably compact, ordered phase of the colloidal particles. The Langmuir monolayer of the platinum clusters was transferred to suitable substrates and analyzed using transmission electron microscopy, quartz crystal microgravimetry and X-ray photoemission spectroscopy. An organized monolayer of platinum clusters was observed indicating that the air-water interface may be used as a medium for obtaining nanoparticle films for device applications.