The grain boundary (GB) migration rate was studied in ice bicrystals obtained from 1 to 10 µmol l(-1) (0.02 to 0.2 ppm) potassium chloride (KCl) water solutions and annealed at temperatures above -20 °C for 170 days. GB mobility was determined as a function of annealing temperature and solute concentration. The GB mobility values obtained show a systematic dependence on the solute concentration. For the first time, it was observed in ice that small concentrations of impurity decrease the GB mobility, as occurs in other materials. The results also indicate possible changes of the GB structure in the annealing temperature range studied.