The present study reports the effect of anionic surfactant sodium dodecyl sulfate (SDS, C12H25 OSO3Na) upon the electrokinetic (electrophoretic mobility, zeta potential) and rheological (viscosity, yield value) properties of the Ca-bentonitic clay found in Turkey and its Na-activated form. The SDS dispersant was added in different concentrations in the range of 1 x 10(-5)-5 x 10(-2) mol/l. The results show that the viscosity and zeta potential values of bentonite dispersion are affected by the addition of anionic surfactant. The obtained data are analysed by considering the kind of exchangeable cations. Thixotropic property effect was observed in bentonite dispersions.