AbstractViscosities of mixtures of poly(vinyl alcohol) and Na smectite in water were measured at several pressures by using Couette and falling‐body‐type viscometers. The values of viscosity of clay‐polymer mixtures were found to bear an exponential relationship to the concentration of the polymer. The viscosities of these mixtures could be related to the concentration of clay by Arrhenius law at low concentrations or by Weltmann and Green's equation at high concentrations. The viscosities of polymer, clay, and clay–polymer mixtures increase exponentially with p