Four kinds of Kaolins (K-1, K-2, K-3 and K-4) from various origins were studied using X-ray diffraction, Si-29 and Al-27 MAS-NMR spectroscopy and scanning electron microscopy (SEM). Mineralogical and morphological characteristics of these samples are given. Kaolinte is the principal mineral but other minerals are present in small quantities: Illite, Muscovite and Quartz. The thermal behaviour of K-1, K-2, K-3 and K-4 was studied. The transformation heats during heating were quantified from DTA measurements and phase changes were followed by X-ray diffraction analyses and Si-29 and Al-21 MAS-NMR spectroscopy. Results indicated that a series of phase transformations take place as the Kaolin is fired at elevated temperature. Mullite is first formed at a temperature as low as 1100 degrees C. Microstructural evolution of this specimen and their mechanical properties are investigated. (C) 2008 Elsevier B.V. All rights reserved.