Tungsten (VI) oxide, WO 3 nanoparticles were synthesized by colloidal gas aphrons (CGAs) technique. The resultant WO 3 nanoparticles were characterized by thermogravimetric-differential thermal analysis (TG-DTA) and X-Ray diffraction (XRD) measurements in order to determine the phase transitions, the crystallinity and the size of the WO 3 nanoparticles. As a comparison, transmission electron microscope (TEM) was used to investigate the size of the WO 3 nanoparticles. The result from XRD and DTA show that the formation of polymorphs WO 3 nanoparticles have the following sequence: orthorhombic (-WO 3 )  monoclinic (-WO 3 )  triclinic (-WO 3 )  monoclinic (-WO 3 ) with respect to the calcination temperature of 400, 500, 600 and 700C. No diffraction peaks were found in the X-Ray diffraction measurements for the sample heat treated at 300C (as-prepared), suggesting that an amorphous structure was obtained at this temperature whereas the crystallinity had been obtained by the other samples of the WO 3 nanoparticles at the calcination temperatures of 400, 500, 600 and 700C. It is also found that the X-Ray diffraction measurements produced an average diameter of (30  5), (50  5), (150  10) and (200  10) nm at calcination temperatures of 400, 500, 600 and 700C respectively by using Debye-Scherrer formula. The TG curve revealed that the WO 3 nanoparticles is purely anhydrous since the weight loss is insignificant (0.3 -1.4) % from 30 until 600C for the WO 3 nanoparticles calcined at 400C. Finally, the composition and the purity of the WO 3 nanoparticles have been examined by X-Ray photoelectron spectroscopy (XPS). The results indicate no significant changes to the composition and the purity of the WO 3 nanoparticle produced due to the temperature variations.