Herein we describe experiments of photocatalytic degradation of Indigo Carmine dye, carried out by new composites containing nanometric SnO2 supported on Al2O3. The composites were prepared in a sequence of procedures which involved reactions of SnBuCl3, aluminium hydroxide with NH4OH in ethanol in order to impregnate organotin oxide in Al2O3 in different stoichiometry. Hence, the obtained materials were employed in experiments of thermal decomposition in O-2 at different temperatures, yielding nanoparticles of SnO2 supported on Al2O3, with ratios of Sn/Al2O3 of 30% (1), 40% (2) and 60% (3) in weight, respectively. XRD experiments revealed diffraction patterns of SnO2, and those of Al2O3 were not observed due to their low crystallinity. Sn-119 Mossbauer experiments suggested the formation of SnO2 in all experiments. Studies of scanning electron microscopies (SEM) showed the formation of tin(IV) oxide on the surface of Al2O3 in composites (1)-(3). The crystallite average size (D) was calculated employing Scherrer equation, revealing the presence of nanometric SnO2 in all samples. Photocatalytic degradation of Indigo Carmine in aqueous medium, induced by composites (1)-(3), was monitored by electronic spectroscopy, and composite (3) displayed the higher activity. In addition, results from electrospray ionization mass spectrometry (ESI-MS) and tandem mass spectrometry (ESI-MS/MS) allowed us to propose a degradation route for the dye. (c) 2010 Elsevier B.V. All rights reserved.