The chemical synthesis is a leading route for the purposeful design of nanomaterials, whereas the tungsten oxides are employed in a variety of special applications. The production of nanomaterials by traditional synthetic methods is still a cumbersome multistep procedure. Here we propose an improved method to produce tungsten oxide nanoparticles via a pyrolytic process. A tungsten-containing precursor was prepared by liquid extraction using n-trioctylamine (C8H17)3N solution in toluene. We have shown that the conditions of thermal treatment of the W-based precursor determine the crystalline structure and nanomorphology of the final product. Monoclinic WO3 nanocrystallites are produced conducting the pyrolysis above 450 °C. The proposed method is a facile and versatile route to produce and control the phase composition and morphology of tungsten oxide-based nanomaterials.