The evolution of electrochemical behaviour and oxide film properties of 304 stainless steel in high temperature aqueous environment have been studied by polarization curves, electrochemical impedance spectra (EIS) and X-ray photoelectron spectroscopy (XPS). The electrochemical data indicate that the corrosion resistance of the steel increases with immersion time. The EIS and XPS analyses show that the oxide films are a duplex structure and the corrosion rate is dominated mainly by the Cr-rich inner layer. The correlation between the evolution of the electrochemical behaviour and the changes of the oxide film properties is discussed.