On the basis of the kinetic study with three kinetic models, this paper predicted mercury adsorption by activated carbon (AC) under an O-2/CO2 combustion atmosphere. Results showed that Bangham's model, pseudo-second-order kinetic model, and Elovich model could describe the mercury sorption process by AC under both O-2/N-2 and O-2/CO2 atmospheres. The kinetic constant k, was the highest at an oxygen concentration of 8% under an O-2/N-2 atmosphere but 4% under an O-2/CO2 atmosphere. The equilibrium adsorbed amount qe was larger under an O-2/N-2 atmosphere than under an O-2/CO2 atmosphere at the same oxygen concentration, and it exhibited great effects on the initial mercury adsorption rate a. The Elovich model verified that the chemical adsorption of active sites was the rate of the control step in the mercury removal on the AC surface. All of these results were very significant for mercury removal under an oxy-fuel combustion atmosphere.