[en] Highlights: • Nb-La-doped SrTiO₃ nano powders were successfully synthesized by the hydrothermal method. • The nano-inclusions and second phases precipitated from matrix to form a complex micro and electron structure. • Record-high ZTs >0.6 at 1000–1100 K were obtained in La-Nb-doped SrTiO₃ bulks. Strontium titanite (SrTiO₃), which is an experimentally-friendly thermoelectric material, could be a promising candidate for thermoelectric power generation applications. The theorectical study indicates the co-doping of La and Nb could enhance the thermoelectric performance, however, the thermoelectric figure of merits (ZTs) of SrTiO₃ are still low because the co-doping process at nano-scale is experimentally difficult to control. Here we report a high performance SrTiO₃ with La-Nb co-doping, which are prepared by a combination of hydrothermal method and high-efficiency sintering. Nano-scale co-doping is successfully modulated by hydrothermal method, and nano-inclusions precipitate during sintering process, to form complex microstructures. In this case, the electrical and thermal transport properties are optimized simultaneously by doping concentration and dopants type, resulting in a record-high ZT >0.6 at 1000−1100 K in the 10 mol% La and 10 mol% Nb doped SrTiO₃ bulk materials. The nano-scale modulation doping and microstructure controlling approach validated in the present study should be also applicable for other thermoelectric materials.