Although the fabrication of nanostructures of various silicides has been widely reported, it is still difficult to fabricate well-aligned and periodic silicide nanostructures, especially for Mg2Si owing to a high vapor pressure and low condensation coefficient of Mg atoms. Periodic Mg2Si nanorod arrays were synthesized by the heat treatment of Si nanorod arrays with porous structure under Mg vapor, reported in the paper by Wen Li et al. on pp. 1796–1799. On the other hand, well-aligned and periodic Si nanorods with 370 nm in diameter and up to 500 nm in height were successfully fabricated on the surface of the Si substrate coated with a thin SiO2 layer under the assistment of monodispersed polystyrene nanospheres. The morphology of the Si nanorod arrays is preserved in the Mg2Si nanorod arrays. The cover figure shows plan-view and cross-sectional images of the nanorod arrays before and after reacting with Mg vapor at 500 °C for 10 min. In the inset of the figure, the nanorods exhibit a porous structure, which are composed of nanosized Si particles. After reacted with Mg vapor, the pores are not observed on the surface of the Mg2Si nanorods. The experimental volumetric expansion from the Si nanorods to Mg2Si nanorods is about V/VSi = 1.55 and the density of the Si nanorods with porous structure is about 48.3%. The periodic Mg2Si nanorod arrays will be useful to control thermal and/or solar radiation.