Highly dense and fine-grained (Sr 1− x Gd x )TiO 3− δ ceramics (x=0.05–0.12) were fabricated by a sol–gel process plus spark plasma sintering, and their thermoelectric properties were investigated from ∼300K to 1100K. The results show that the electrical resistivity of the (Sr 1− x Gd x )TiO 3− δ ceramics decreases greatly while maintaining large absolute value of the Seebeck coefficient |S| upon Gd doping. As a result, a large power factor (PF) greater than 10μWcm −1 K −2 is obtained in (Sr 0.9 Gd 0.1 )TiO 3− δ in the temperature range from 400K to 1000K, and peak PF reaches 16μWcm −1 K −2 at ∼570K. Simultaneously, the lattice thermal conductivity κ L reduces remarkably (e.g. κ L decreases from 2.7 to 2.13Wm −1 K −1 at ∼1000K). Owing to the large PF and low κ L , a record value of figure of merit ZT=0.37 is achieved at 1006K for (Sr 0.9 Gd 0.1 )TiO 3− δ , indicating that appropriate combinations of fine-grained microstructure with both high densities and proper doping as well as oxygen deficiency are essential to the effective enhancement of thermoelectric performance of STO-based ceramics.