This paper introduces the preparation of needle-shaped cuprous oxide (Cu2O) particles 3-10 nm in diameter and 40-150 nm in length on multiwall carbon nanotubes (MWNTs) by anodic oxidation of copper electrode in alkaline solution. Steady-state concentration of H2O2 as high as 0.42 mM is produced in aqueous suspension of nanosized Cu2O/MWNTs composites illuminated by simulated solar light in the presence of formate and oxygen. Assisted by Fe2+-EDTA, these photogenerated H2O2 can be used as Fenton reagent; hydroxyl radicals have been detected indirectly. The results for the degradation of brilliant red dye indicate that the effect of this new Fenton system (1 g/L nanosized CU2O/MWNTs composites + Fe2+-EDTA + simulated sun light) can approach that of traditional Fenton system (4 mmol/L H2O2 + Fe2+-EDTA). This system is superior to the classical Fenton system in that it can act effectively for a long time. (c) 2005 Elsevier B.V. All rights reserved.