The characteristics of NOx (NO and NO2) and NH3 adsorptions and their impacts on As2O3 adsorption on gamma-Al2O3 are essential for the development of catalyst protection technologies in the selective catalytic reduction (SCR) process. Mechanisms of the mentioned adsorption processes are calculated via density functional theory (DFT) in this study so as to reveal adsorption structures and other features. According to DFT calculation results, both NOx and NH3 could convert the physisorption structures from oxygen atoms of the first layer to chemisorption structures (with only one exception). In the meantime, other original chemisorption structures still belong to chemisorption even though their adsorption energies decrease a little. This phenomenon resulted from the different adsorption positions of NOx and NH3 on the surface of gamma-Al2O3 and the changes of band structures incurred by the significantly increased electronegativity and nearby hydrogen bonds. Contents of this study could provide helpful information for understanding the behavior of gamma-Al(2)O(3 )in the context of the SCR process.