Abstract: The buffer/backfill performance of bentonite-based materials may be affected by the influences of temperature fields, thereby leading to uncertainties in the safe operation of repositories. In order to address this issue, the swelling tests on Gaomiaozi (GMZ) bentonite are carried out in distilled water at 25, 40, 60, and 90 °C. The results show that the swelling of GMZ bentonite increases with the temperature, owing to that the osmotic swelling dominates the swelling of compacted GMZ bentonite under the experimental conditions. The maximum swelling strain increases linearly with the temperature, whereas the swelling pressure increases exponentially with the temperature. The swelling characteristics of compacted GMZ bentonite can be expressed as e_m=Kp^D-3. According to the results of N₂ adsorption tests, the fractal dimension, D, of GMZ bentonite is unaffected by the temperature. Calculated by the diffuse double layer model under osmotic swelling, a linear relation is found between the montmorillonite swelling coefficient K and the temperature Tc, which is verified by the swelling tests on GMZ bentonite and Bikaner bentonite. Combining the linear K−T_c relation and the fractal e_m-p relation, a simple method for evaluating the swelling of GMZ bentonite affected by the temperature is proposed.