The growth kinetics of passivating oxide film of Inconel alloy 600 has been investigated in aqueous 0.1 M Na2SO4 solution at temperatures 25-300degreesC and at pressures 0.1-8 MPa by analyses of potentiostatic current transients and ac impedance spectra. From the analysis of current transients, it was realized that the oxide film grown on the specimen has only one-layer structure below 60degreesC, but it is composed of two layers with different structures, i.e. an inner layer and an outer layer, above 100degreesC. In addition, ac impedance spectra exhibited one capacitive loop below 60degreesC, but they exhibited two capacitive loops above 100degreesC. This substantiates that the structure of the oxide film changed from one-layer structure below 60degreesC to two-layer structure above 100degreesC. Moreover, from the analysis of ac impedance spectra, it was found that the value of the apparent specific resistivity of the inner layer decreased with rising solution temperature, but that value of the apparent relative permittivity increased. (C) 2003 Elsevier Ltd. All rights reserved.