Alloy nanoparticles in the Mg-Al system were prepared by plasma arc discharge method from the Mg-x to Al (45% < x <65 wt.%) bulk alloys. Powders were produced at various applied voltages. High purity argon and helium were separately employed as cooling and carrier gases. Morphology, composition, phase structure and particle size of the products were investigated by field emission scanning electron microscopy (FESEM), inductively coupled plasma-atomic emission spectroscopy (ICP-AES), X-ray diffraction (XRD) and dynamic light scattering (DLS) techniques. Morphological studies show the formation of spherical nanoparticles with smooth surface. Higher voltages (related to electrode gap distance) accompanied by helium as cooling gas provide finer nanoparticles. Because of difference in evaporation rates for both magnesium and aluminum in the master alloy, the compositions of synthesized powders are found to be different from those of the raw materials. Three crystalline phases including Mg, Al and Al12Mg17 are detected in prepared powders. Oxide phases are not detected in XRD pattern. The DLS studies demonstrate the mean particle size of 52 and 160 nm related to powders synthesized under helium and argon atmosphere, respectively. (C) 2014 Elsevier B.V. All rights reserved.