The mass transfer processes in REUSY zeolites and fluid catalytic cracking (FCC) catalyst particles have been measured and distinguished in this study by uptake method with an intelligent gravimetric analyser (IGA) and by the frequency response (FR) technique. The results indicate that the diffusion time constants in the FCC catalyst particles are smaller than those in the REUSY zeolites, and the limiting steps for the overall mass transfer processes in the FCC catalyst particles are the diffusion process in the length scale of macropore of the matrix or/and the mass transfer at the zeolite-matrix interface rather than the intracrystalline diffusion one in the micropores of the zeolite crystals. Crown Copyright (C) 2014 Published by Elsevier B.V. All rights reserved.