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Stainless steels are one of the most promising materials as bipolar plates for polymer electrolyte membrane fuel cells (PEFCs). In use of stainless steel bipolar plates, however, corrosion and corrosion induced degradation of cell performance are anticipated. In the present study, corrosion behavior of SUS 304 and 31 OS stainless steels was investigated through polarization tests in the simulated PEFC environment (0.05M NazS04 (pH 2.3) + 2 ppm F solution at 353 K), contact resistance measurement between steels and carbon diffusion layer and cell operation. XPS analysis was also carried out to compare the steel surfaces after polarization measurements and cell operation. The results indicated that passive current density for SUS 310S stainless steel in the simulated PEFC environments was lower than that for SUS 304 stainless steel, as expected from higher Cr content. Longer polarization of these steels decreased the passive current density but increased contact resistance due to thickening of the passive film. The cell voltage drops after 3.6 x 10 6 s operation were 14 mV for graphite, 22 mV for SUS 310S and 46 mV for SUS 304 steel. Apparent corrosion was recognized for SUS 304 stainless steel served for cathode.