Nitrate ion has contaminated surface water and underground water resources, especially in rural areas. Nitrate ion and its derivatives, especially nitrite ion, are harmful to human health. Various methods such as ion exchange resin, reverse osmosis, and biological nitrogen dehydration have been used for removal of ion nitrate. Photocatalytic process decomposition is an efficient method for degradation of organic and inorganic pollutants and their conversion into minerals. Nanocatalysts of Cu-TiO 2 / Bi 2 O 3 have been synthesis as a cheap and new photocatalyst for the reduction of nitrate ion. TiO 2 , Cu-TiO 2 and Cu-TiO 2 /Bi 2 O 3 nanocatalysts were synthesized by sol-gel method. Reduction of nitrate ion was treated with visible and UV radiation. Nanocatalyst of Cu-TiO 2 /Bi 2 O 3 was coated on a glass-plate by dip-coating method, and the nitrate ion degradation was measured by thin films of nanocatalyst. In this study, effect of the independent properties of pH, Cu / Ti ratio, and Bi 2 O 3 /TiO 2 ratio on efficiency of reduction of nitrate ion under visible radiation were studied and their values were optimized using the CCD method. The result of this optimization was achieved by removal nitrate ion yield of 16.6% nitrate ion for pH = 2, Cu/Ti ratio of 1.4% and Bi 2 O 3 /TiO 2 ratio of 6.9%. By using optimum condition and UV radiation, the efficiency of nitrate ion reduction was 74% and the reasons for the difference in the efficiencies of nitrate ion reduction were investigated. Also by designing thin layer film reactor and under visible radiation, nitrate ion removal efficiency was experienced at 13%. Synthesized nanocatalysts were characterized by XRD, FE-SEM and DRS.