We report a facile green method for in situ synthesis of Mg/CuO core/shell nanoenergetic arrays on silicon with Mg nanorods as the core and CuO as the shell. Mg nanorods are first prepared by glancing angle deposition. CuO is then deposited around Mg nanorods by reactive magnetron sputtering to realize the core/shell structure. Various characterization techniques are used to investigate the prepared Mg/CuO core/shell nanoenergetic arrays including scanning electron microscopy, transmission electron microscopy, x-ray energy dispersive spectroscopy, x-ray diffraction, and thermal analyses. Uniform mixing and intimate contact between Mg nanorods and CuO are confirmed both from visual inspection of morphological images and analyses of heat release curves. The nanoenergetic arrays exhibit low onset reaction temperature (~300 °C) and high heat of reaction (~3400 J/g). Most importantly, the nanoenergetic arrays possess long-term storage stability due to the stable CuO shell. This study provides a potential general strategy for synthesis of various Mg nanorods based stable nanoenergetic arrays.