A simple modification in hot filament chemical vapour deposition has been used to control the growth of tungsten oxide nanoparticles on a large scale where the as-deposited material is mostly amorphous in nature with a few nanoparticles. However, upon annealing in air, almost all the material converts into spherical nanoparticles with a low size dispersion as characterized by TEM. X-ray diffraction, XPS and PL were used for structural, compositional and optical analysis.