Effective La-doped SrTiO₃ (Sr_1−xLa_xTiO₃, x = 0–0.1 mol.% La-doped) nanocubes were successfully synthesized by a hydrothermal method. The influence of different La dopant concentrations on the physicochemical properties of the host structure of SrTiO₃ was fully characterized. X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD) revealed that the Sr²⁺ in the crystal lattice of SrTiO₃ was substituted by La³⁺. As a result, the absorption region of the Sr_1−xLa_xTiO₃ could be extended to visible light. Scanning electron microscopy (SEM) images confirmed that their morphologies are associated with an increased surface area and an increased La-doping concentration. The decrease in the photoluminescence (PL) intensity of the dopant samples showed more defect levels created by the dopant La⁺³ cations in the SrTiO₃ structure. The photocatalytic activities of Sr_1−xLa_xTiO₃ were evaluated with regard to the degradation of 2-naphthol at typical conditions under artificial solar light. Among the candidates, Sr_0.95La_0.05TiO₃ exhibited the highest photocatalytic performance for the degradation of 2-naphthol, which reached 92% degradation efficiency, corresponding to a 0.0196 min⁻¹ degradation rate constant, within 180 minutes of irradiation. Manipulating the structure of Sr_1−xLa_xTiO₃ nanocubes could produce a more effective and stable degradation efficiency than their parent compound, SrTiO₃. The parameters remarkably influence the Sr_1−xLa_xTiO₃ nanocubes’ structure, and their degradation efficiencies were also studied. Undoubtedly, substantial breakthroughs of Sr_1−xLa_xTiO₃ nanocube photocatalysts toward the treatment of organic contaminants from industrial wastewater are expected shortly.