Mg 2 Si and Mg 2 Si incorporating oxides such as Al 2 O 3 , ZrO 2 , SnO 2 , ZnO, B 2 O 3 and CuO were formed by using a spark-plasma sintering (SPS) technique. The "oxide-incorporated" Mg2Si samples exhibited the formation of voids and also clusters of oxide materials. The effects of oxide incorporation into Mg 2 Si were investigated in an attempt to identify oxides that exhibit lower thermal conductivity but an equal power factor and figure-of-merit when compared with pure Mg 2 Si. In the cases of the samples of Mg 2 Si that incorporated SnO 2 , ZnO, ZrO 2 and Al 2 O 3 , the observed power factors showed no significant temperature dependence, with values comparable to those observed for pure Mg 2 Si at about 2×10 -5 W/cmK2. The incorporation of SnO 2 or ZnO improved the lattice thermal conductivity over the whole measured temperature range when compared with a pure Mg2Si sample. The observed deviations in the values of the figures-of-merit between the SnO2- or ZnO-incorporated Mg 2 Si and the pure Mg 2 Si (without the oxide) were observed as being rather small, with no remarkable dissidence in the measured values. It was realized that the SnO 2 - and the ZnO-incorporated Mg 2 Si samples exhibited thermal conductivity values that were more than 20 % lower than that of pure Mg2Si at around 773 K.