Hydrothermal reaction by using ammonium mobium oxalate as a precursor was performed to prepare cellulose acetate/Nb2O5 catalyst with the following Nb2O5 loadings (in wt%) 3.9, 5.8, 6.7 and 10.9. These materials presented homogeneous dispersion of niobium on cellulose acetate surface with Bronsted and Lewis acid sites based on SEM/EDS microscopy and infrared spectroscopy. The thermal stability of these catalysts was at least 210 degrees C and these composites were applied as photocatalyst to degrade indigo carmine dye in water. This catalytic behaviour was followed though a kinetic series adjusted to a Langmuir-Hinshelwood equation. The kinetic constants obtained by application of this equation were 2.95, 3.47, 3.63 and 3.98 mu mol L-1 h(-1) for CA/Nb 3.6, 5.8, 7.4 and 10.9%, respectively. The materials were reused nine times more to degrade indigo carmine dye. (c) 2005 Elsevier B.V. All rights reserved.