The modification of kaolinite hydroxyl surfaces of both ordered and disordered kaolinites has been studied under a range of conditions and intercalating agents, This has been achieved by the study of the kaolinite hydroxyl deformation vibrations by the application of diffuse reflectance Fourier transform infrared (DRIFT) spectroscopy. Kaolinites showed resolved bands at 940 and 915 cm(-1) with an additional band at 923 cm(-1). The bands at 940 and 923 cm(-1) are assigned to the hydroxyl deformation modes of the inner surface hydroxyl groups, and the 915 cm(-1) band is assigned to that of the inner hydroxyl group, When the kaolinite is intercalated with potassium acetate additional bands were found at 909 and 897 cm(-1) for the ordered kaolinites. An additional band at 877 cm(-1) is observed for the disordered kaolinite and is attributed to the hydroxyl deformation mode of non-hydrogen-bonded hydroxyl groups. The bands at 909 and 897 cm(-1) range are attributed to inner surface hydroxyl groups hydrogen bonded to water or acetate groups, The intensity of these bands reflects the degree of disorder introduced into the kaolinite through intercalation, The intensities of the kaolinite hydroxyl deformation modes are a function of the starting kaolinite order and the method of preparation.