Ni2+-exchanged zeolite P has been used as a heterogeneous catalyst in the photodecolorization process of Eriochrome Black T dye in aqueous solution under UV irradiation. The effect of various experimental variables such as catalyst dosage, solution temperature, initial concentration of the dye and initial pH of the dye solutions were studied on the decolorization efficiency. The optimal operational parameters were found as follows: pH 9, 0.8 g L-1 catalyst loading, 30 ppm dye concentration. The effect of zeolite was also tested and the obtained results showed that there was no considerable decolorization in the presence of Ni2+ in solution as a homogeneous catalyst. The decolorization process obeyed first-order kinetics. (C) 2010 Elsevier B.V. All rights reserved.