The oxidation of aniline has been performed in the liquid phase at moderate temperatures over a series of transition-metal-substituted molecular sieves. Experimental data have shown that TS-1 was not the best catalyst for this reaction but that large pore zeolites or mesoporous silicas were preferred. Indeed, these solids could be used with either hydrogen peroxide or tert-butyl hydroperoxide (TBHP) as oxidant. For low oxidant/aniline ratios, azoxybenzene (AZY) was the major product formed over Ti-containing catalysts, but azobenzene (AZO) and nitrosobenzene (NSB) were also detected. The selectivity in AZO was always higher with TBHP than with H2O2. In contrast, V-substituted zeolites were only active with TBHP and led to the very selective formation of nitrobenzene.