Large crystals of the ZSM-5 type zeolite were dealuminated with several methods in order to compare the effectiveness of various ways of treatment and its influence on the fractal dimension (D) of the obtained materials. Some of the adsorption isotherm equations based on the Polanyi-Dubinin potential theory appeared to he useful Cor the description of the benzene adsorption on the examined materials, They can be accepted a,, suitable for characterising the distribution of the adsorption potential and adsorption energy in the MFI-type molecular sieves. Evaluation of D from the benzene adsorption data indicated that there was no evident correlation between the fractal dimension and the level of dealumination. It means that the adsorbed benzene was not sensitive to any surface roughness of zeolites of the MFI-structure type. (C) 2002 Elsevier Science B.V. All rights reserved.