The magnetic properties, the magnetostriction, and the magnetoelectric effect in the -electron free rare-earth aluminum borate are investigated between room temperature and 2 K. The magnetic susceptibility reveals a strong anisotropy with the hexagonal axis as the hard magnetic axis. Magnetostriction measurements show a large effect of an in-plane field reducing both the -axis and -axis lattice parameters. The magnetoelectric polarization change in and directions reaches up to at 70 kOe with the field applied along the axis. The magnetoelectric polarization is proportional to the lattice contraction in magnetic field. The results of this investigation prove the existence of a significant coupling between the rare-earth magnetic moment and the lattice in compounds ( earth). They further show that the rare-earth moment itself will generate a large magnetoelectric effect which makes it easier to study and to understand the origin of the magnetoelectric interaction in this class of materials.