The paper presents the results of an experiment on the synthesis of aluminum-magnesium spinel nanoparticles using an electric arc plasmatron. Metal powders of aluminum and magnesium were used as raw materials. The metal powder particles burned almost completely, ensuring the appearance of the desired oxides in the gas phase, which is a necessary condition for the synthesis of nanoparticles. As a result, a weakly agglomerated nanopowder of the composition Al-Mg spinel (~mass52%), Al2O3 (~mass32%) and MgO (~mass16%) in the cubic phase was obtained, having a narrow size distribution (17 nm at half maximum) and a particle diameter of 10 nm at maximum of distribution functions.