Heterogeneous photo-Fenton process using an amorphous FeOOH as catalyst was studied to degrade Methyl Orange (MO) dye in aqueous solution. The amorphous FeOOH was prepared by dissolution and precipitation using a high iron-containing fly ash as raw material. The ash not only provided iron source but also acted as a supporter of amorphous FeOOH. Coating the fly ash particles with the amorphous FeOOH significantly enhanced the removal of MO, and 2.5 g of catalyst was sufficient to degrade 50 mg MO from 1 I of aqueous solution at pH 7.0 after 80 min. Oxidant concentration, solution pH. UV/dark/sunlight and recycling of the catalyst were investigated in order to evaluate the photo-Fenton effects. Moreover, variations of particle size before and after preparation, separation of solid-liquid and stability of the amorphous FeOOH in the catalyst were studied. It was testified that the amorphous FeOOH on the surface of fly ash was stable and the Fenton catalyst was easily separated from the aqueous system. (C) 2009 Elsevier B.V. All rights reserved.