The possibility of reducing the size of bulk materials, particularly making nanoparticles with controlled size, structure and shape offers massive benefits for various applications. In this respect, we report a novel water-assisted method to produce clusters of WO2 nanopowders with very high conversion yields of 90%. The proposed process is simplistic in its nature and carried out at room temperature. Nanopowders were obtained as a result of the hydrolysis of the tungsten precursor (WCl6) in the presence of NaBH4. Particle sizes of the as-synthesised partially crystallized nanopowders show a uniform distribution around 35 nm. Fully crystallized nanopowders without any morphological alteration were successfully produced already after annealing at 500 degrees C for 2 h. The nanopowders were examined using electron microscopy, XRD and DSC. (C) 2014 Elsevier B.V. All rights reserved.