The effect of aluminum introduction into the zinc ferrite ZnFe2-xAlxO4 spinel structure was studied in the concentration range of 0.0 less than or equal to x less than or equal to 1.0. Spinel ferrites were obtained by hydrothermal method at 140 degrees C in the whole range of Al concentration (x). The resulting powders were calcined at 550 and 750 degrees C, and their physicochemical and catalytic properties were compared with those prepared by coprecipitation method [J.A. Toledo, P, Bosch, M.A. Valenzuela, A. Montoya, N. Nava, J. Mol. Catal, 125 (1997) 53]. As in coprecipitated samples, isomorphic substitution of Fe3+ by Al3+ into the octahedral sites was observed. The aluminum introduction gives rise to a lattice distortion caused by the introduction of a metal with smaller atomic radius. This lattice distortion facilitates a charge transfer from Fe3+ to O2-, which increases the basicity of the oxygen atoms in the Fe-O-Al bonds, increasing its proton affinity. Therefore, it favors the acid-base dissociation that takes place in the C-H bond during the abstraction of the hydrogen atom in the oxidative dehydrogenation (OXD) process. After calcination at 550 degrees C, a maximum in the intrinsic activity and butadiene yield was obtained for an Al concentration of 0.2 less than or equal to x less than or equal to 0.5, whereas in coprecipitated catalysts, a higher aluminum content was necessary (0.75 less than or equal to x less than or equal to 1.0). In the hydrothermally treated samples calcined at 750 degrees C, the promoter effect of aluminum was not evident. Indeed, the pure ZnFe2O4 showed the maximum activity to butadiene. However, the activity of the structural surface sites increased by a factor about 2 as the calcining temperature increased from 550 to 750 degrees C,