A Ni/Mg(Al)O catalyst was obtained from a composite NiMgAl lamellar double hydroxide precursor. This material was tested in the gas-phase hydrogenation of acetonitrile between 353 and 423 K, after calcination and reduction at various temperatures. The highest selectivity to monoethylamine, 94.6% at 47% reactant conversion, was reached after calcination at 623 K and reduction at 723 K. FTIR spectroscopies of adsorbed CD3CN and CO were carried out on the reduced sample. The adsorption of CD3CN provided evidences that the acidity of Ni/Mg(Al)O was the lowest after calcination at 623 K and reduction at 723 K. Depending on the activation treatment, the vco of (Ni)(x)CO, at low CO coverage, took different values reflecting some modifications of the Ni d-band. The increased selectivity in monoethylamine in the hydrogenation of acetonitrile on Ni/Mg(Al)O was correlated with the decrease of acidity of the sample, and not with a modification of the electronic properties of Ni. The decrease of the acidity of the support lowered the acid-catalysed transamination reaction leading to secondary and tertiary amines.