Some organophilic montmorillonites (OPMNTs) have been synthesized from Na-montmorillonite (Na-MNT) using ammonium salts of methyl, propyl, butyl, and dodecyl amine. Thermogravimetric (TG), infrared (IR), and X-ray analyses of the compounds were carried out. Microstructural parameters such as crystallite size and root mean square strain (rms) (<e 2 > 1 / 2 ) have been calculated by X-ray line profiles analysis. TG analysis in the temperature range 20-100 o C show a weight loss for pure Na-MNT and OPMNTs of about 11% and 2.8%, respectively, indicating the organophilic properties of the OPMNTs. IR and X-ray analyses confirm the formation of OPMNTs by an ion exchange reaction. It is also observed that the crystallite size and rms strain increase with increase carbon number (n c ) in the amines.