Strontium titanate nanoparticles were synthesized by a microwave-assisted solvothermal reaction of SrCl 2 ·6H 2 O, Ti(OC 3 H 7 ) 4 in KOH methanol–oleic acid solution. The products were characterized by TG-DTA, XRD, TEM, BET surface area and XPS. The photocatalytic activity was determined by DeNO x ability using LED lamps with various wavelengths such as 627nm (red), 530nm (green), 445nm (blue) and 390nm (UV). The nanoparticles of perovskite type SrTiO 3 with the particle size of 15–18nm were successfully synthesized. The photocatalytic activity of SrTiO 3 under visible light (λ=530nm) irradiation could be generated by modification of the surface with the carboxyl group (–COO) from oleic acid which enabled the absorption of visible light.