Al 2 O 3 bicrystals containing [0001] symmetric tilt Σ7 grain boundaries with different grain boundary planes of {45¯10} and {23¯10} were fabricated by diffusion bonding, and the grain boundary structures were investigated by high-resolution transmission electron microscopy (HRTEM). From HRTEM observations combined with atomistic simulations, it was found that the grain boundaries exhibited characteristic atomic arrangements, and the Σ7/{23¯10} boundary contained large open spaces at its core. In compressive creep experiments for the bicrystals, these boundaries showed quite different creep behavior, although they have the same Σ value. The measured sliding rate of Σ7/{23¯10} was much larger than that of Σ7/{45¯10}, which may be due to the open core structure formed in Σ7/{23¯10}.