Destruction of chlorinated aromatic compounds was carried out over mesoporous Cu x Mg 1−x Al 2 O 4 spinel oxides with x=0, 0.2, 0.5 and 0.8, which were prepared by the coprecipitation method. All the catalyst samples were characterized by means of X-ray diffraction (XRD), scanning electron microscopy (SEM) and nitrogen adsorption–desorption isotherms. The performances of these catalysts on the decomposition of hexachlorobenzene (HCB) and the catalytic formation of polychlorinated dibenzodioxin and dibenzofuran (PCDD/F) were evaluated in a closed system. The activities of these catalysts for dechlorination of HCB increased with increasing the magnesium content in them. The Cu 0.2 Mg 0.8 Al 2 O 4 presented a higher catalytic activity for the hydrodechlorination of HCB than CuO, Al 2 O 3 , as well as the other Cu x Mg 1−x Al 2 O 4 spinels. More than 99% dechlorination efficiency of HCB was achieved at low temperatures (≤300°C) for a short time (30min) under air atmosphere over Cu 0.2 Mg 0.8 Al 2 O 4 spinel. In comparison to air atmosphere, nitrogen atmosphere seemed to be more beneficial for the dechlorination of HCB with a dechlorination efficiency of 90% at 250°C for 10min. For the Cu 0.2 Mg 0.8 Al 2 O 4 catalyst, the I-TEQ of PCDD/F formed was 4.5pg/g, far below the value of 15122.5pg/g on CuO. The Cu 0.2 Mg 0.8 Al 2 O 4 catalyst inhibited the chlorination reaction and enhanced the dechlorination reaction. The catalytic behavior including catalytic dechlorination of HCB and catalytic formation of PCDD/F related to the physical characteristics of Cu x Mg 1−x Al 2 O 4 spinel was discussed.