We demonstrate the synthesis of perovskite oxide SrTiO3 with ideal cation stoichiometry and homogeneous La doping using air-stable Sr-Ti and La-Ti bimetallic peroxo complexes with a 1:1 cation ratio. Phase-pure SrTiO3, La2Ti2O7, and LaTiO3 were successfully synthesized by thermal decomposition of those complexes. La-doped SrTiO3 was obtained by mixing the Sr-Ti and La-Ti complexes in an acid solution, followed by thermal decomposition. La-doped SrTiO3 showed systematic chemical trends in the lattice constant and electrical conduction. Not only those bulk polycrystals but also cation-stoichiometric SrTiO3 epitaxial thin films were grown with an atomically flat surface from the Sr-Ti complex.