Lanthanum and nitrogen co-doped SrTiO₃ was synthesized using polymerized complex method with Ti(OC₃H₇)₄, SrCl₂·6H₂O and La(NO₃)₃·6H₂O as starting materials followed by calcinations in NH₃. Ethylene glycol and anhydrous citric acid were used as the precursors of synthesis. The samples were characterized using XRD, TEM, DRS, BET, EDX and XPS. The cubic-perovskite type of La/N co-doped SrTiO₃ nanoparticle could be successfully synthesized. The photocatalytic activity of SrTiO₃ for DeNO_x ability in visible light region (λ > 510 nm) could be improved by co-doping of La³⁺ and N^3_. The high visible light photocatalytic activity of this substance was caused by a narrow band gap energy that enables to absorb visible light.