In this study, the rheologic and colloidal characterizations of sodium montmorillonite (NaMMT) were examined. Hexadecylamine (CH3(CH 2)15NH2, HDA) was added to the bentonite water dispersion (2%, w/w) in different concentrations in the range 5-6 × 10-4-9-4 × 10-3 m mol/1. The Theological and electrokinetic behaviour of aqueous montmorillonite dispersions was investigated as a function of solid content and HDA concentration. The basal spacings of the HDA/NaMMT composites were studied by X-ray diffraction. The FTIR spectra were obtained from the modified bentonite products, which revealed the characteristic absorbances after treatment with HDA. © Indian Academy of Sciences.