A series of oxide ceramics with the general formula of Sr1-xLaxNb2O6-δ (x = 0.1, 0.2, 0.3, 0.4) was synthesized and the characterization was study in detailed. The XPS results reveal that the heterovalent substitution of La3+ for Sr2+ leads to the Nb4+ dominated chemical state in this series of oxides, and a mass of oxygen vacancy defects exist in the oxides after annealed in strong reduction atmospheres. Due to increased phonon scattering by lattice distortion and heavier La atoms, all of the samples achieve lower thermal conductivity. The electrical resistivity and the magnitudes of Seebeck coefficient monotonically decrease with the increase of the content of lanthanum. Overall, the sample of Sr0.6La0.4Nb2O6 reaches the maximum ZT of ∼0.13 at 1073 K.