The effect of exchange cations (Mn+: Li+, Na+, K+, NH4 +, Ca2+, Mg2+, Fe3+, and Al3+), and thermal treatment on the physicochemical properties of smectite was investigated. Before thermal treatment, unheated (25°C) Mn+-smectite showed increased d001 spacing on glycol solvation, after heating at 300°C or above (400°C) d001 spacing on glycol solvation of Al-, Fe-, Mg-, Li-smectite decrease and reached 10Å, however, d001 of Ca2+-, Na+- and NH4 +-smectite increase upon glycol salvation indicated that d001 varied with the nature of exchangeable cation and the temperature of heating. The results generally suggested that: d001 of homoionic smectite before and after heating at various temperatures depended upon the nature of exchangeable cation. The cation exchangeable capacities (CEC) and the BET surfaces area (SBET) were functions of the type of exchangeable cations, since SBET drop off in the following order: Na+-smect>Ca2+smect>Mg2+-smect>NH4 +-smect>Li+-smet>K+-smect >Fe3+-smect>Al3+-smect. Finally we have noted a good progress in exchangeable properties of synthesized clay comparatively with the Na homoionic smectite form, except the K homoionic clay witch present the lowest CEC and SBET, consequently the lowest exchangeable properties.