The photocatalytic degradation of textile diazo dye Naphthol Blue Black has been investigated using sunlight and Ce1-xMnxO2 (x=0, 0.1, 0.2, 0.3 and 1.0) samples. Ce1-xMnxO2 samples were synthesized by co-precipitation method and characterized by XRD, FTIR, thermal techniques and surface areas. Some solid-state studies, such as magnetic susceptibility, electrical resistivity and diffuse reflectance studies were undertaken. The extent of decolourization of the dye was determined by UV-vis spectroscopy. CeO2 forms solid solution with Mn upto 30 mol% maintaining fluorite structure. (c) 2007 Elsevier B.V. All rights reserved.