n-Type TiO2/p-type Cu2O nanodiode photocatalyst with different Cu2O contents had been successfully synthesized. The nanocomposite also had been well characterized and tested for its photocatalytic activity toward reduction of 10 ppm K2Cr2O7 aqueous solution under visible light illumination. It was found that 30 % Cu2O loading in the nanocomposite had the best photocatalytic activity in detoxifying Cr(VI) without any hole scavenger agents and the solution pH adjustment. As a result, water was simultaneously oxidized by photogenerated holes to evolve oxygen. The 20 mg as-prepared TiO2/Cu2O nanocomposites could reduce almost 100 % of 10 ppm K2Cr2O7 aqueous solution in 90 min under 150 W halogen lamp illumination. From the results, it was concluded that the photocatalytic activities of p-n heterojunction of TiO2/Cu2O nanodiodes had proven to be an efficient photocatalyst under visible light illumination. The photocatalytic performances of TiO2/Cu2O nanocomposites and its photoreaction mechanism were proposed and discussed in this work.