Changes in the hydroxyl surfaces of cesium acetate intercalated kaolinite have been studied over the ambient to predehydroxylation temperature range using a combination of FTIR and Raman spectroscopy, combined with X-ray diffraction. Upon intercalation of a low-defect kaolinite with cesium acetate, the kaolinite layers expanded to 14.0 Angstrom. Upon heating the intercalate to 50 degreesC, the kaolinite expands to 17.0 Angstrom. Over the temperature range 100-200 degreesC, a third phase with a d(001) spacing of 12.80 Angstrom was observed. These expansions are reversible, and upon cooling the intercalation complex and upon exposure to air for sufficient lengths of time, the d(001) spacing returned to 14.0 Angstrom. These expansions are in harmony with thermal decomposition measurements. Diffuse reflectance spectroscopy shows that the cesium acetate intercalated kaolinite is almost completely intercalated and that the thermal treatment of the intercalate is reversible. The Raman spectrum of the hydroxyl stretching region of the intercalated kaolinite showed a new band at 3606 cm(-1), which was attributed to the inner surface hydroxyl hydrogen bonded to the acetate ion, Mild heating of the intercalated complex to 50 degreesC caused a rearrangement of the surface structure with a Raman band being observed at 3610 cm(-1). It is proposed that the 3610 cm(-1) band is associated with the 17.0 a phase and that the 3606 cm(-1) band is associated with the 14.0 Angstrom phase. Further thermal treatment over the 100-200 degreesC temperature ranges resulted in two hydroxyl bands at 3618 and 3609 cm(-1). The 3618 cm-l band is attributed to the inner hydroxyl. At the predehydroxylation temperature for cesium acetate intercalated kaolinite (similar to 300 degreesC), two bands were observed at 3609 and 3619 cm(-1). Above this temperature, no hydroxyls are spectroscopically evident. Upon cooling to room temperature, the Raman spectra of the hydroxyl surfaces are identical to that of the initial intercalation complex, showing that the thermal modification of the kaolinite surfaces is reversible. The thermal treatment results in some minor deintercalation.