Tungsten nanoparticles have been synthesized by the chemical reaction route. Reduction of WO3 with the in situ produced hydrogen gas at 600 degrees C in current work is a new approach for the production of W nano-powder. The results of XRD show that nanostructure alpha-W and beta-W is present in the final product. Differential thermal analysis (DTA) showed the beta ->alpha phase transition occurs around similar to 435 degrees C. The morphology and particle size distribution of tungsten nanosized powders have been analyzed by scanning electron microscope (SEM) and transmission electron microscope (TEM). The results show that an average crystallite size of product W nanopowder is about 32 nm. (c) 2013 Elsevier B.V. All rights reserved.