Natural kaolin was treated at 850 or 950 degrees C in air flow to give respectively the metakaolin samples MK8 and MK9. The obtained materials were successively treated at 90 degrees C with a 1 M solution of H2SO4, for various time lengths. The acid treatment of MK8 was found to give a high surface area microporous material with good catalytic properties related to the high density of acid sites, while MK9 gave an ordered mesoporous material with a low density of acid sites. The materials were characterized by several techniques, X-ray powder diffraction, thermogravimetric analysis, N-2 physisorption, scanning electron microscopy, and temperature-programmed desorption of ammonia. The I-butene isomerization was used as test reaction to evaluate the acidity of the samples. (c) 2007 Elsevier Inc. All rights reserved.