Oxidation of acidic dye Eosin Y has been investigated with Fenton process and photo-Fenton process (solar light or artificial light source). With UV-Fenton process and Fenton, 42.5% and 21.3% of dye could be removed from the water, respectively. However, 94.1% of dye was removed in solar-Fenton in 90 min. Based on solar-Fenton process, the effect of pH value and the concentration of dye, Fe2+, H2O2 as well as oxalic acid concentration on Eosin Y degradation efficiency were investigated. In 60 min, 96% of Eosin Y was degraded when the pH value was 3.5 and the concentration of Fe2+, H2O2 and oxalic acid was 10 mol/L, 600 mg/L and 300 mg/L, respectively. The Eosin Y degradation was dependent on the dye concentration. That is higher Eosin Y concentration resulted in lower degradation efficiency. Under the conditions of pH 3.5, the Eosin Y apparent kinetics equation was -dC/dt = 0.000249[Eosin Y](0.78)[Fe2+](1.14)[H2O2](1.26). Meanwhile, this research also proved that oxalic acid could improve the photocatalytic efficiency in the solar-Fenton process. (c) 2007 Elsevier B.V. All rights reserved.