The effect of an external electric field on the grain-growth behavior of acceptor Mg-doped, undoped, and donor Nb-doped BaTiO3 ceramics was investigated. The acceptor-doped and undoped specimens showed enhanced grain growth at the positive-biased region. On the other hand, for the highly donor-doped specimens, grain growth was enhanced in the negative-biased region. The results have been explained in terms of defect polarization and the consequent change in the boundary potential. It has been suggested that liquid penetration into grain boundaries is critically dependent on the boundary potential.