The change of grain boundary internal friction peak during high temperature deformation at different modes (i.e., static tensile creep, cyclic tensile creep, and cyclic reverse torsion) in high purity aluminum was studied in conjunction with microstructure examinations. It was observed that the internal friction peak decreased with increasing plastic strain for all the modes, indicating that grain boundary sliding was degraded by the deformation. Nevertheless, at the same strain the decrement of internal friction was different for different modes, in particular smallest for reverse torsion. The origin of the decrease of internal friction and the difference among different modes is interpreted in the light of microstructure observations.