Emanation thermal analysis (ETA) is based on the measurement of the rate of release of radon from solid samples previously labelled with trace concentrations of an inert radioactive nuclide (Thorium-228 or Ra-224). This method enables pointing out of the different steps that occur during the heating of kaolinite : pre-dehydroxylation, dehydroxylation, evolution of structural disorder in metakaolinite, segregation of amorphous silica and formation of precursors of high-temperature phases, crystallization and sintering of both mullite and cristobalite. The investigations of two kaolinite samples of quite different crystallinity demonstrates the role of the structural disorder of the mineral in the manifestation of these structural changes. The differences observed between the behaviour of the two samples are reflected by different diffusivities of radon which can be related to different morphology changes taking place in kaolinite during heating. The results obtained demonstrate the potential of ETA as a complementary method of conventional thermoanalysis and XRD methods.