We report on an effective increase in the Seebeck coefficient for 5% La-doped SrTiO3 nanoceramics at temperatures of 300-800 K through grain boundary doping with Nb, which results in an improvement of power factor by a value as high as 35%. This enhancement is likely due to the energy filtering effect at the Nb-doped grain boundaries with an enhanced potential barrier originating from the band offset between the boundaries and the interior of the grains. (C) 2013 Elsevier B.V. All rights reserved.