Abstarct: In this project, the synthesis of tungsten oxide nanoparticles and the study of its properties as an active laxyer in an electrochromic device were considered. Initially, the synthesis of tungsten oxide nanoparticles using Oxalic acid as the surface agent was performed by acid precipitation method, and then a modified solution combustion synthesis (SCS) was used for nanoparticles synthesis. Nine samples were resulted by using the solution combustion synthesis of tungsten oxide nanoparticles. The effect of various fuels, as well as the role of the hotplate, microwave oven, and furnace as heating sources, was studied on the structural and microstructural properties of prepared nanoparticles. The Oxalic acid, Citric acid and Glycine used as the fuels. X-ray diffraction pattern of synthesized nanoparticles identified the orthorhombic structure for WO3.H2O nanoparticles and the monoclinic, tetragonal and amorphous structures for WO3 nanoparticles. SEM Images exhibited the various size and morphology for synthesized nanoparticles. Three samples of HG, MG, and FG were selected to use as the electrochromic laxyer considering the structural and microstructural considerations. The selected samples made the sputtering targets and were used to deposition thin films with 300nm thickness on FTO-glass and ITO-glass substrates by RF sputtering. In addition, the synthesis and deposition of PANI and PANI-WO3 nanocomposite were done and the electrochromic properties of the samples were investigated using the three-electrode Cyclic Voltammetry. The Ag/AgCl was used as a reference, the Pt as a counter, and the electrochromic thin film as a working electrode. Electrochemical intercalation/deintercalation of ions and electrons exhibited the visible coloration of the samples. The transmittance of the bleach and dark state revealed that the HG-FTO-PVA sample has a poor electrochromic property with a 12% changing in transmittance. In contrast, the MG-ITO-PVA sample with a 71% loss of transmittance has the best electrochromic response.