The mobility of grain boundaries under certain conditions is a key factor for the evolution of polycrystalline microstructures and material properties. In recent experiments it was shown that grain boundaries can interact with mechanical stress fields and that the motion of planar grain boundaries, low angle as well as high angle grain boundaries, could be induced by an external mechanical stress field [1,2]. Therefore the current study was performed to investigate the details of grain boundary motion and interactions between definite, planar grain boundaries and the mechanical stress field during high temperature low cycle deformation of high purity aluminium bicrystals. The grain boundary planes were in all cases perpendicular to the loading axis. Experiments were made with large as well as small stresses at different temperatures and numbers of cycles. The displacement of grain boundaries was measured by using optical microscopy, and the microstructural features, as well as orientations of individual grains were recorded by the electron backscatter diffraction technique (EBSD) after each deformation experiment.