Al-doped ZnO ceramics were fabricated by the electrical field-assist sintering method and their thermoelectric properties were examined. When the current density of 10A/cm2 was applied, the electrical conductivity was increased by about 30 % compared with that of a specimen set in the same furnace without any applied current. The Seebeck coefficient was also increased by approximately 10%. The power factor was thus improved about 60%, reaching 1.3x10-3 W/mK2 at 1053K, which is one of the best power factor in bulk oxides. Analyses of Hall measurement and thermal conductivity showed that longer mean free paths of both electrons and phonons were obtained by the electrical field-assist sintering method, suggesting promotion of the grain growth and/or reduction of barriers at the grain boundary in the direction of current.