This study deals with the role of the alumina nanoporous texture in the accessibility of the asphaltene molecules to the active sites of resid hydroconversion catalysts. We have proposed in this contribution to investigate the diffusion and adsorption process into the porosity of various monomodal and bimodal alumina supports. It consists of immersing catalytic supports, under the form of extrudates, into an asphaltene solution in toluene. Optical microscopy observations of a cut of the cylindrical extrudates were carried out to follow the asphaltene penetration as a function of the contact time. We aimed at reaching a good asphaltene mass balance, taking into account (i) the evolution of the asphaltene concentration in solution and (ii) the precise determination of the amount of asphaltenes deposited into the support. The influence, on the mass transfer and the penetration depth, of various parameters such as temperature, asphaltene concentration of the solution, asphaltene size polydispersity, and alumina porous texture was appraised. The novelty of this Article resides in the evaluation of diffusion and adsorption of asphaltenes at high temperature (250 degrees C). Finally, an endeavor for the process modeling is presented. The adsorption equilibrium was modeled according to the Langmuir-type isotherm. A model considering the radial diffusion in a cylinder (the extrudate) was used providing an average diffusion coefficient.