Several Ni/Mg/Al and Ni/Al hydrotalcite-like precursors have been prepared to study their catalytic properties in the hydrodechlorination of 1,2,4-trichlorobenzene in the gas phase. All the samples were characterised by X-ray diffraction (XRD), BET, scanning electron microscopy (SEM), temperature-programmed desorption (TPD) and hydrogen chemisorption techniques. When the magnesium content increases in the catalysts, both the activity and selectivity to benzene greatly increases and the deactivation of the catalysts becomes slower. The highest TOF and selectivity to benzene values at 523 K (100%) are achieved by the catalyst which has the most content of Mg without any significant change in activity even at reaction times higher than 500 min. This catalytic behaviour can be explained because the MgO modifies the electronic properties of the nickel particle causing the hydrogen desorption at lower temperatures and also adsorbs the HCl produced during the hydrodechlorination reaction.