High-quality thermochromic monoclinic VO2(M) and series of W-doped V(1-x)W(x)O2(M) nanoparticles were successfully synthesized by an improved thermolysis method. The products were investigated using X-ray diffraction (XRD), transmission electron microscope (TEM), X-ray photoelectron spectroscopy (XPS), differential scanning calorimetry (DSC) and Fourier transform infrared spectroscopy (FTIR) technologies. The measurement of DSC revealed that the metal-insulator phase transition (MIT) of 2.0% W-doped VO2 sample occurred at 25.6 degrees C, which was much lower than the MIT of host VO2(M) nanoparticles at 67.6 degrees C. The results showed that the proportion of the transmittance of tetragonal phase reached only about 29% of that of monoclinic phase for 0.5% W-doped VO2 at the wavenumber 900 cm(-1), which indicated W-doped VO2(M) was an intelligent window and optical switch materials.