During the last decade oxide-based thermoelectric materials have received increased attention due to their high stability and thermal robustness at high temperatures as well as the availability and nontoxic nature of a number of promising candidates. In the present study we are investigating the thermoelectric properties of an n-type La-substituted SrTiO 3 with the specific composition (La 0.12 Sr 0.88 ) 0.05 TiO 3 . Nanosized powder precursors were spark plasma sintered (SPS) for 5 minutes between 900 and 1,200°C, resulting in densities between 73 and 98% and crystallite sizes between 40 nm and 1 μm. The formation of a rutile phase (TiO 2 ) was observed in samples sintered at 1,150 and 1,200°C; at lower temperatures only single-phase cubic perovskite was observed. There was no clear evidence that the presence of rutile affected the thermal conductivity (κ). A significant reduction in κ was observed both with increasing porosity and reducing crystallite size, showing a minimum at~700°C corresponding to~1.3 W m −1 K −1 .