The present study investigated the effects of particle size on the adsorption performance of tungsten oxide nanoparticles. Nanoparticles 18–73 nm in diameter were prepared by evaporation of bulk tungsten oxide particles using a flame spray process. Annealing plasma-made tungsten oxide nanoparticles produced particles with diameters of 7–19 nm. The mechanismof nanoparticle formation for each synthetic route was examined. The low-cost, solid-fed flame process readily produced highly crystalline tungsten oxide nanoparticles with controllable size and a remarkably high adsorption capability. These nanoparticles are comparable to those prepared using the more expensive plasma process.