The influence of cationic surfactants benzyldimethyltetradecyl ammonium chloride (BDTDACl) and dodecyltrimethylammonium bromide (DTABr) on flow behaviors and electrokinetic properties of soda activated bentonite suspensions (3 wt.%) were studied. Surfactants were added to the bentonite water system in different concentrations in the range of 10(-5) - 10(-2) mole/L. The interactions between clay minerals and surfactants in water-based Na-activated bentonite dispersions (3 wt.%) were examined in detail using rheologic parameters, such as viscosity, yield point, apparent and plastic viscosity, hysteresis area, and electrokinetic parameters of mobility and zeta potentials, and XRD analyses also helped to determine swelling properties of d-spacings. Besides, the influence of pH and particle size distributions was also evaluated. XRD studies revealed that d-spacings expanded about 1.98 and 3.49 angstrom after the interactions of bentonite + DTABr and bentonite + BDTDACI complex, respectively. (c) 2005 Elsevier B.V. All rights reserved.