Abstract The aim of this work was to study the thermal behavior of carboxymethyl cellulose (CMC) aqueous solutions and bentonite-CMC mixtures, from room temperature to higher temperatures, above gelation, using a rheological analysis. The rheological properties of aqueous CMC solutions and bentonite-CMC dispersions at different mass concentrations of CMC (0.1, 0.5, 1.0 and 2.0 wt%) were investigated at different temperatures (20, 40, 60 and 80 °C) using large deformation rheological measurements. Viscosity measurements show that for both CMC solutions and bentonite-CMC dispersions sudden changes in viscosity occur as the temperature increases. The viscosity is found to decrease below a critical temperature which corresponds to a cloud point or gelation temperature. Above this later, the viscosity increases dramatically with temperature. Hydrophobic interaction is postulated to be the cause of gelation.