Iron corrosion products (ICPs) were tested as heterogeneous catalysts to decolourize orange II (OII) in the presence of oxalic acid under simulated natural light or solar light. ICPs were collected from the cast iron pipes used in a wastewater treatment plant, and characterized with energy dispersive X-ray spectroscopy (EDS). X-ray powder diffraction (XRD) and N-2 adsorption/desorption isotherm analyses. The photodecolourization efficiency depends significantly on various factors including the ICPs dosage, initial concentration of oxalic acid and the initial pH value. Under the optimal conditions (ICPs dosage 0.40 g/L, initial concentration of oxalic acid 1.6 mM and pH 3.0), the photodecolourization efficiency for a solution of 25 mL containing 10 mg/L OII reaches 83% and 44%, respectively, under simulated natural light (I = 14 mW/cm(2)) and solar light (I = 1.2 mW/cm(2)) for 30 min. Tartaric or citric acid is also efficient for ICPs to photodecolourize OII under simulated natural light. Since this system directly uses ICPs as heterogeneous catalysts and does not require the addition of hydrogen peroxide and shows good efficiency even under solar light, it is an economically viable method for decolourization of wastewaters containing dyes. (C) 2012 Elsevier B.V. All rights reserved.