The presence of CrO₄^2- induced increase in negative surface charge and decrease in positive surface charge of two variable charge soils. The effect on positive surface charge increased with the decrease in pH, while an opposite trend was observed for negative surface charge. The effect also increased with the level of CrO₄^2- added. The mechanism of the effect may involve adsorption of CrO₄^2- in the soils, because with the change in soil surface charge, CrO₄^2- adsorption occurred in the soils. The quantity of CrO₄^2- adsorbed by the soils also increased with the decrease in pH and the increase in level of CrO₄^2- added, which was generally consistent with the change of soil surface charge.