The bentonite from gaomiaozi county (Inner Mongolia, China) (GMZ bentonite) has been selected as the candidate of backfill material in China for nuclear waste repository. Herein, the sorption of 90Sr(II) on GMZ bentonite was investigated as a function of contact time, solid content, pH, ionic strength, foreign ions, humic acid (HA) and temperature. The results indicated that the sorption of 90Sr(II) was mainly dominated by ion exchange or outer-sphere surface complexation at low pH, whereas inner-sphere surface complexation was the main sorption mechanism at high pH values. The thermodynamic parameters (ΔH0, ΔS0 and ΔG0) calculated from the temperature-dependent sorption isotherms indicated that the sorption of 90Sr(II) on GMZ bentonite was an endothermic and spontaneous process. The results provided important information for the interaction mechanism of 90Sr(II) with GMZ bentonite, and is crucial for the evaluation of GMZ bentonite as backfill material.