The stress induced migration of planar grain boundaries in aluminium bicrystals was measured. Symmetrical <100> tilt grain boundaries with misorientation angles in the range between 5.7° and 17.8° were examined. Boundary migration under a shear stress was observed to be ideally coupled to the lateral translation of grains. The measured ratios of the normal boundary motion to the lateral displacement of grains are in an excellent agreement with the respective boundary geometry. The temperature dependence of grain boundary mobility was measured, and the corresponding activation parameters were determined. The activation enthalpy of boundary migration was found to be independent of misorientation angle in the investigated misorientation range and amounts to H=1.44 eV.