A quartz crystal microbalance technique was used in conjunction with Auger electron spectroscopy to characterize the oxides formed on a number of different Fe‐Cr alloy thin films oxidized in air at 300 °C. Data was also obtained on pure iron and chromium thin films. The oxide thickness varied almost linearly with chromium concentration between 15 and 45 wt. %. Logarithmic growth kinetics persisted for chromium and iron‐chromium films whereas parabolic kinetics were found for the iron films. The chromium film kinetics were comparable to those of the Fe 20 wt. % alloy.