Cu/Mg/Al mixed oxides (CuO = 4.0-12.5 wt%), obtained by calcination of hydrotalcite-type (HT) anionic clays, were investigated in the selective catalytic reduction (SCR) of NO by NH3, either in the absence or presence of oxygen, and their behaviours were compared with that of a CuO-supported catalyst (CuO = 10.0 wt%), prepared by incipient wetness impregnation of a Mg/Al mixed oxide also obtained by calcination of an HT precursor. XRD analysis, UV-visible-NIR diffuse reflectance spectra and temperature-programmed reduction analyses showed the formation, in the mixed oxide catalysts obtained from HT precursors, mainly of octahedrally coordinated Cu2+ ions, more strongly stabilized than Cu-containing species in the supported catalyst, although the latter showed a lower percentage of reduction. The presence of well dispersed Cu2+ ions improved the catalytic performances, although similar behaviours were observed for all catalysts in the absence of oxygen. On the contrary, when the mixture with excess oxygen was fed, very interesting catalytic performances were obtained for the catalyst richest in copper (CuO = 12.5 wt%). This catalyst exhibited a behaviour comparable to that of a commercial V2O5-WO3/TiO2 catalyst, without any deactivation phenomena after four consecutive cycles and following 8 h of time-on-stream at 653 K. Decreasing the copper content or increasing the calcination time and temperature led to considerably poorer performances and catalytic behaviours similar to that of the CuO-supported catalyst, due to the side-reaction of NH3 combustion on the free Mg/Al mixed oxide surface.