Zinc bicrystals with originally flat < 10 (1) over bar0 > 89 degrees symmetric tilt boundary tilted at similar to 45 degrees to the tensile direction were strained at high temperature. The operation of crystallographic slip in both grains was suppressed by orientation of basal planes parallel and perpendicular to the tensile axis. The boundary migrated under the action of curvature driving force making its inclination angle close to 70 degrees with respect to the lateral free surface. In the case of annealing with no load applied, a small boundary migration was observed at the edges of the sample. Initiation of grain-boundary sliding significantly increases the amount of boundary migration. It has been established that sliding can increase the reduced boundary mobility by more than an order of magnitude.