A theory for the steady state viscosity&eegr;of thixotropic clay‐water suspensions is given. The numerical results of this analysis can be approximated byu + u2/10 = K/&ggr;˙whereu = (&eegr;r − 1)/C, &ggr;˙is the shear rate,&eegr;∞is the viscosity for&ggr;˙ → ∞, &eegr;r =&eegr;/&eegr;∞, andKandCare parameters depending on concentration and temperature. For large shear rates this expression reduces to the Bingham behavior&eegr;r = 1 + &tgr;0/&eegr;∞&ggr;˙, where&tgr;0is the Bingham yield stress. Experiments on a Wyoming bentonite at various concentrations and temperatures give good agreement with the theoretically predicted behavior. The comparison of experimental and analytical results yields the cohesive force per particle and the ratio of the major and minor dimensions of the bentonite particles.