We present a strategy for increasing thermoelectric performance by invoking ferroelectric distortion in a transition-metal oxide. By using an ab initio calculation approach with the Boltzmann transport equation, a large Seebeck coefficient is calculated in n-type BaTiO3. The polar structural distortion causes the peculiar dispersion of the lowest conduction band, which enhances the Seebeck coefficient along the polar direction. A microscopic mechanism of carrier concentration dependence of the Seebeck coefficient is discussed in terms of the band velocity distribution in the Brillouin zone. ; Comment: 6 pages, 6 figures, submitted to JPSJ