In this study, the effect of the two cationic surfactants (benzyldi-methyltetradecyl ammonium chloride (BDTDACI) and dodecyltrimethylammonium bromide (DTABr)) on the electrokinetic and rheologic properties of Na-montmorillonite dispersion (3% w/w) has been investigated at their concentrations between 0 and 10 mmol/L. Experimental results reveal that cationic surfactants are attached on the surface of negatively charged clay particles and also they penetrate into the interlayer of clay particles. The intercalation of surfactants with clay minerals is shown to lead to an increase in the interlayer spacing of montmorillonites by X-ray diffraction. The Fourier transform infrared (FTIR) spectra obtained from the modified bentonite products reveal the characteristic absorption bands. The morphology of bentonite dispersions was analyzed by scanning electron microscopy (SEM). Both X-ray diffraction data and scanning electron micrographs of intercalated montmorillonites indicate that most of the montmorillonites are dispersed randomly in the organo-clay dispersion.