Abstract: Pure and Ce-doped nano-TiO₂ particles were prepared by a sol-gel process and characterized and explained by UV-Vis and XRD spectra. Being a model reaction, the photocatalytic degradation of methyl orange aqueous solution in the present of CeO₂/TiO₂ nano-particles was investigated with a high pressure mercury lamp as the light source. The results show that rare-earth Ce doped makes the reflective spectral characteristic of nano-TiO₂ move to the visible region with a red shift to 500 nm, and is favorable to enhancing the absorption of visible and UV light of nano-TiO₂. A few Ce⁴⁺ doped enter into the crystal lattices of TiO₂, but a lot of Ce⁴⁺ doped disperse into TiO₂ or cover onto TiO₂ as the form of CeO₂ with small size. It is indicated that rare-earth Ce doped increases its photocatalytic activity, and the optimum molar fraction of Ce in CeO₂/TiO₂ is 2.0%.