In this investigation, Gd-CoSeO3 nanocomposite with controlled Gd doping contents was synthesized using a sol gel method. The resultant specimen was found to have large specific surface area (115 m(2)/g) and limited particle size (15 nm). TEM examination illustrated that the synthesized Gd-CoSeO3 nanocomposite exhibited nanospherical morphology. Also, it was revealed that band gap controlling of the CoSeO3 nanoparticles could be accomplished via managing the Gd contents. The photocatalytic activity of the Gd-CoSeO3 nanocomposite samples was inwctspected via Nitrobenzene - aniline transformation applying visible light irradiation. Gadolinium doping was adopted to improve the photo-catalytic of the synthesized CoSeO3. This can be accredited to band gap decrease of CoSeO3 by Gd doping as well as life time increase of e-h recombination rate which occur via electron trapping by Gd metal. Therefore, we can prepare an efficient photocatalyst by sol-gel method and photoassisted deposition method to control band gap and e-h recombination rate.