A series of molecular dynamics simulations was performed to study grain boundary sliding of three types of [101¯0] tilt grain boundaries in a magnesium bicrystal. In particular, a near Σ11 twin boundary, an asymmetric near Σ11 twin boundary, and a θ = 40.3° general [101¯0] tilt grain boundary were studied. Simulations showed that grain boundary sliding (a rigid motion of two grains relative to each other along boundary plane) did not occur over the stress range applied; instead, coupled shear motion (grain boundary sliding induced boundary migration) was dominant. Although the measured coupling coefficient, the ratio of boundary tangential displacement to boundary normal displacement, was in good agreement with theoretical prediction, the detailed shear behavior was different, depending on types of grain boundary, magnitude of applied shear stress, and temperature. It was also noted that grain boundary twining was the predominant mechanism that allowed the coupled shear motion to occur in hexagonal close-packed (HCP) magnesium.