Ceramics of LaxSr1-xNbyTi1-yO3 (LSNT) were synthesized under various reducing atmospheres. Covering the specimens with graphite carbon felt under an Ar-gas flow during sintering drastically enhanced the electrical conductivity, sigma. Ti K-edge absorption spectra indicated the presence of Ti3+ for heavily reduced specimens. The increase in conductivity was attributed to the 3d band of Ti3+. The maximum value for the figure of merit, ZT, was obtained for strontium titanate ceramics modified with both 5mol% La and 5mol% Nb, namely 5/5-LSNT, exhibiting a ZT value of similar to 0.221 at 473K. This high ZT value was almost 1.5xlarger than that of the conventional 10mol% La-doped sample, 10/0-LSNT (ZT similar to 0.144), and was mainly attributed to the larger Seebeck coefficient of the material.