Synthesis of Ca3Co4O9 and CuAlO2 ceramics for thermoelectric application using areaction-sintering process were investigated in this study. Without any calcination involved,the mixture of raw materials was pressed and sintered directly. Decomposition of Ca3Co4O9 at926oC limited a sintering temperature above 926oC. Ca3Co4O9 formed as the major phase andsome minor phases Co3O4, CaCo2O4, and Ca2Co2O5 were also found in Ca3Co4O9. A maximumdensity value 2.46 g/cm3 was found at 900oC/6 h sintering. Very weak peaks of unreactedAl2O3 were detected in CuAlO2. Density of CuAlO2 ceramics reached a maximum value 4.1g/cm3 at 1350oC/2 h. The reaction-sintering process has proven a simple and effective methodin preparing Ca3Co4O9 and CuAlO2 ceramics for thermoelectric application.