The hydrodealkylation of 1,2,4-trimethylbenzene (1,2,4-TMB) was investigated on partially reduced Ni–Al mixed oxide catalysts prepared by the co-precipitation method. The catalytic performances of these Ni–Al mixed oxides were considerably influenced by different factors, such as the molar ratio of Ni/Al, calcination temperature of the catalysts, etc. The sample with a Ni/Al molar ratio of 1:8 calcined at 500°C (denoted as NiAl 8 -500) showed the highest activity and total selectivity to lighter aromatics with a 62.3% conversion and a 60.2% selectivity to xylene. Characterization results showed that the unreduced NiAl 8 -500 catalyst mainly consisted of pseudo-spinel like solid solution (NiAl 2 O 4 ), and could produce monodispersed nickel atoms (Ni(0)), which are closely associated with alumina sites (Lewis acid) upon reduction. We propose that the relatively high hydrodealkylation activity of the NiAl 8 -500 catalyst could be mainly assigned to the presence of a number of neighboring metallic Ni(0) atoms and Lewis acidic sites.