Polycrystalline La-doped CaMnO3 ceramics have been prepared by a solid-state sintering method. Analysis of microstructure and phase composition indicates that the addition of La can prohibit the further growth of grain, and no impurity phase appears. The results revealed that the La doping can lead to a large change of the activation energy (from 0.22 to 0.02 eV), and thus result in a marked increase in electric conductivity of 2-4 orders of magnitude. The power factor can reach about 1.5×10-4 W·m-1·K-2 in a wide temperature range, which potentially make them attractive for n-type high-temperature thermoelectric materials.