Abstract: Activated meso-carbon microbeads (a-MCMBs) as a kind of new carbon materials can store and purify natural gas.The diffusion of methane and carbon dioxide in a-MCMB prepared by the authors, was investigated by using the intelligent gravimetric analyzer apparatus (IGA-003, HIDEN) at 298 K and 258 K.The diffusion coefficients of methane and carbon dioxide were correlated in terms of the Fick diffusion model.The results indicated that the diffusion of methane and carbon dioxide in a-MCMB was intra-crystalline diffusion and the diffusion coefficients were of the order of magnitude 10^-13 m²·s^-1.Moreover, the diffusion coefficients of methane and carbon dioxide in a-MCMB all increased with temperature and decreased with pressure.In addition, the diffusion coefficients of methane were larger than those of carbon dioxide in a-MCMB at the same temperature and pressure.This conclusion is useful in studying the mass transfer process in the applications of a-MCMB as the adsorbent.