The corrosion behavior of weathering steel and carbon steel exposed in marine atmosphere for 4 years were studied by means of regression analysis, rust structure observation, X-ray diffraction, Raman spectrum and electrochemical impedance spectra techniques. The results show that the corrosion procedure of weathering steel is divided into two steps. In the first step, the corrosion rate is higher, while in the second step the corrosion rate is remarkably reduced due to a compact rust layer formed gradually during exposure. The compact rust layer on weathering steel, darkened observed using polarized light, is composed of Cr substitute iron oxyhydroxide. Furthermore, an equivalent circuit is set up to represent the interfaces between rusted steels and 3% NaCl solution, and the rust layer resistances of the steels were deduced from an extrapolation of the electrochemistry impedance spectra to estimate the protective properties. (C) 2002 Elsevier Science B.V. All rights reserved.