The effect of the concentration of reactant on the deactivation of chromium oxide catalysts for the oxidation of CVOCs was investigated. Feeds with various PCE concentrations of 30, 1,000, 5,000 and 10,000 ppm were introduced into the reactor for the oxidation over CrOx catalysts supported on high surface area TiO2 and Al2O3 . Both chromium oxide catalysts exhibited stable PCE removal activities up to 100 hours of reaction time without any catalyst deactivation at the low concentration of PCE in the feed, 30 ppm. However, high concentrations of PCE, from 1,000 to 10,000 ppm, significantly deactivated the chromium oxide catalyst regardless of the support. Deactivation of the chromium oxide catalyst was neither caused by the evaporation of chromium from the catalyst surface nor the reduction of surface area by coking. It was mainly due to the phase transformation from Cr(VI), active reaction sites on the catalyst surface, to Cr(III). Although some of Cr on the catalyst surface evaporated during the course of the reaction at high feed concentrations of PCE, it was insignificant to reduce the PCE removal activity of the catalyst.