La0.8Ce0.2MnO3 perovskite catalyst was employed for elemental mercury (Hg-0) oxidation in coal combustion flue gas. The effects of flue gas components, including O-2, NO, SO2, HCl, H2O as well as the selective catalytic reduction (SCR) reductant (NH3), on Hg-0 oxidation were investigated systematically. Above 90% Hg-0 oxidation was obtained at 200 degrees C under simulated flue gas (SFG) and SCR atmosphere with a gas hourly space velocity of 60,000 h(-1). Gaseous O-2 regenerated and replenished surface oxygen, hence promoting the oxidation of Hg-0. NO promoted the Hg-0 oxidation because of the formation of active surface species like NO2. HCl facilitated the Hg-0 oxidation, and 98.8% Hg-0 oxidation was obtained under the atmosphere containing 10 ppm HCl in the co-presence of O-2. SO2 inhibited Hg-0 oxidation because of the irreversible damage on catalytic activity by reacting with the active species on the catalyst center dot H2O also inhibited Hg-0 oxidation due to the change of catalyst surface chemistry as well as the consumption of active surface chlorine species (Cl*). NH3 competed active sites with Hg-0 and induced oxidized mercury reduction, hence limiting the Hg-0 conversion. However, the inhibitive effect of NH3 could be partly offset by the promotional effect of NO. This work clarified the effects of flue gas compositions on Hg0 oxidation over a novel La0.8Ce0.2MnO3 perovskite catalyst, which is essential for further improving the catalyst activity.