Abstract: Using F127 as template agent, tetraethyl orthosilicate as silicon source, a series of mesoporeous silica FDU-12s as model catalysts were synthesized under different conditions for investigation of diffusivity of asphaltene. The catalysts were characterized by BET，XRD，TEM，SEM techniques. The influence of assemble temperature and crystallization temperature on the pore size of the materials was investigated. The diffusivities of asphaltene in the catalysts with different pore size were studied. The results show that rising the crystallization temperature can only enlarge the pore mouth size of FDU-12 molecular sieves without the increase of cage diameter, while lowering the assemble temperature has a opposite effect. Increase of entrance pore size and cage size of FDU-12 enhances the effective diffusivity; however, the decrease of specific surface due to excessive increase of pore size can reduce effective diffusivity.