Air drying of sintered spheres of glass beads was investigated under vacuum as well as at atmospheric pressure for comparison. The critical moisture contents at pressures of 0.97-26.7 kPa were close to that at atmospheric pressure. Nevertheless, their mechanisms were different. The drying rate curves for the falling rate period were predicted from a receding evaporation front model with either a two-step moisture distribution in the pendular state or a flat moisture distribution in the pendular state. The predicted as well as the observed drying rate curves for the falling rate period at pressures of 0.97-1.47 kPa decreased either by two stages or monotonically, depending on the shape of the respective moisture distributions. At subatmospheric pressures such as 13.0 and 26.7 kPa, it was, however, difficult to determine the configuration of the water.