Mn–Zr mixed oxide materials have been prepared by a sol–gel method from a Mn (III) precursor salt and a solution of zirconium acetate in acetic acid, being characterized from a structural and morphological point of view. Conventional solid state techniques show that as obtained powders are formed by mixtures of manganese and zirconium acetates and (hydro) oxides, which evolve to bixbyite, hausmannite, as well as tetragonal and monoclinic zirconia above 873 K. Zirconium enhances the formation of the non-thermodynamically stable manganese compounds instead of the thermodynamically stable ones. This effect was not observed in other samples previously prepared by coprecipitation. In general, mixed systems are thermally stable up to 1073 K due to the formation of a solid solution phase of 10% Mn into zirconia, and display higher specific surface areas than those prepared by the coprecipitation method. Their activities in the combustion of heavy aromatic molecules are higher than those of the pure manganese oxides, very likely due to a synergic effect of zirconium. Moreover, the catalytic properties of hausmannite and bixbyite phases for burning this type of hydrocarbons seem to be very similar.