This paper aims at characterization of different cationic forms of montmorillonite clay using FTIR, XRD and TGA techniques. Montmorillonite was separately treated with different alkaline and alkaline earth and transition metal cations, such as Na +, K +, Mg 2+, Ca 2+, Ni 2+, Cu 2+, Zn 2+ and Cd 2+ to get the corresponding homoionic forms of montmorillonite clay mineral. The developed samples were characterized by the above mentioned methods. FTIR spectra of the samples revealed that the exchangeable cations have a minor effect on the stretching and bending bands of the structural OH, while a major one on both position and intensity of the physically adsorbed water was reported. XRD showed the changes in the crystallographic spacings of montmorillonite clay mineral due to ion exchange process. Thermogravimetric study of the examine samples showed two DTG exothermic peaks in their DTG curves, attributed to the dehydration of the physically adsorbed and bounded water and dehydroxylation of the structural water respectively. All the results obtained proved that these exchangeable cations dominated the amount of the physically adsorbed water and initial humidity of the clay. © 2011 IEEE.