The flow properties of natural Ca bentonite and Na bentonite-water systems were studied after adding an anionic polyacrylamide (PAM) polymer. The effect of the PAM has also been investigated at different quantities. The experimental results are discussed in terms of bentonite forms and concentration of PAM. Besides, measurement of theological properties of Ca bentonite + PAM and Na bentonite + PAM systems have been examined in detail through XRD, FT-IR and DTA analyses. (C) 2001 Elsevier Science B.V. All rights reserved.