The intercalation complex of a kaolinite from Cornwall, UK, with dimethylsulfoxide (DMSO) was studied by high-temperature X-ray diffraction (HTXRD), differential thermal analysis (DTA) and thermogravimetry (TG). The X-ray pattern obtained at room temperature indicated that intercalation of DMSO into kaolinite caused an increase of the basal spacing of kaolinite from 7.14 to 11.19 Å. Heating between 25 and 300°C caused the removal of the DMSO, which occurred over several stages. In a first stage (25–125°C), an expansion (from 11.19 to 11.28 Å) followed by a contraction (from 11.28 to 11.19 Å) is observed, at the same time as the intensity of the basal reflection decreased and was replaced by a broad band extending from ~11 to ~7 Å. In a second stage (125–200°C), the loss of DMSO did not lead to changes in the HTXRD patterns; and finally, in a third stage, the loss of DMSO caused an important increase in intensity and sharpening of the basal reflections of the kaolinite. These stages were also shown by the DTA-TG curves for the complex. The TG curve indicated that the loss of ~15% of the intercalated DMSO occurs below 150°C, and caused the disruption of the structure. The remaining molecules, forming stronger bonds with the kaolinite surfaces, were lost between 150 and 300°C.