The knowledge of transport properties in heterogeneous catalysis is of important interest since the selectivity and the activity depend significantly on diffusion. Pulsed Field Gradient (PFG) NMR has proved to be a valuable tool to probe the intracrystalline diffusion of molecules adsorbed in microporous solids [1]. This technique can also be used to study the diffusion in mesoporous materials, such as MCM-41 [2]. In this case, the root mean square displacement of the diffusing molecules during the observation time ∃ is usually larger than the particle diameter and the purely intracrystalline diffusivity Dintra can only be attained using a "two region" model involving the intra- and interparticle spaces [1,3]. In this work we use PFG NMR to study the influence of the pore diameter, the hydrophobicity of the pore surface and the adsorbate concentration on the intraparticle diffusion of n-hexane in MCM-41 solids.