A model using the ideal adsorbed solution theory (IAST) coupled with the micropore-size distribution (MPSD) concept is proposed to describe the multicomponent adsorption equilibrium and kinetics of gases in activated carbon. To overcome the thermodynamic violation, the IAST instead of the extended Langmuir equation was used to calculate the local multicomponent adsorption equilibrium. The micropore size is related to the adsorbate-adsorbent interaction energy by the Lennard-Jones potential. The overall adsorption isotherm and the diffusion flux of the adsorbed species are the integrals of their corresponding local values over all micropore-size distribution range accessible by the adsorbate molecules. The size exclusion effect was taken into account in the competition of different sized molecules for a given pore. The model predictions were tested with the adsorption kinetics data of binary gases on Ajax and Norit activated carbon. The results were better than predictions of a previous multicomponent adsorption kinetics model also using the MPSD concept, but with the local multicomponent adsorption isotherm described by the extended Langmuir equation.