Characterization and catalytic activity of the NiW-based catalysts supported on Al-Ti(x) mixed oxides has been obtained. The results from the characterization techniques (Surface area, XRD, DRS, TPR, XPS, FTIR of adsorbed NO and HREM) were used to establish a relationship between the morphological and structural changes of the tungsten phases and catalytic activity. The results indicate that the incorporation of titania to the support enhances the reducibility and sulfidability of the tungsten phases due to mainly a reduced interaction of the tungsten phases with the support. Correlation of the catalytic activity in the thiophene HDS reaction and the number of tungsten atoms in edge and corner positions in the WS2 crystallites indicates that only the number of tungsten atoms equivalent to those present in one layer of the WS2 crystallites are active at a given time.