An Fe2O3 (10 wt%)/Al2O3 (90 wt%) catalyst prepared by a coprecipitation method was found to be effective for dehydrogenation of ethylbenzene to produce styrene in the presence of CO2 instead of steam used in commercial processes. The dehydrogenation of ethylbenzene over the catalyst in the presence of CO2 was considered to proceed both via a one-step pathway and via a two-step pathway. CO2 was found to suppress the deactivation of the catalyst during the dehydrogenation of ethylbenzene.