The surface composition and depth profile of vanadium dioxide thin films prepared by the sol-gel processing were investigated by using X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES) techniques. It was shown from both XPS and AES results that the VO2 phase was obtained after thermal treatment under vacuum (6.67 Pa) at 500 degrees C for 2 h. The optical transmittance of VO2 thin films changed greatly below and above the phase transition temperature. Doping of Li+ into VO2 thin films resulted in a reduction of the transition temperature. in contrast, Al3+ doped VO2 thin films had a higher transition temperature at 72 degrees C. V0.99P0.01O2 thin films had a similar phase transition temperature to that of undoped VO2 thin films.