Ca3Co4O9 samples synthesized from micrometer (CaCO3 and Co3O4) and nanometer (CaO and Co3O4) sized precursors have been prepared by solid state reaction, sintered by spark plasma sintering. Their thermoelectric properties at high temperature have been studied (650–1000 K). Using one nano-sized precursor seem to allow synthesis of Ca3Co4O9 particles with smaller average size (