Periodic Mg2Si nanorod arrays were synthesized by the heat treatment of Si nanorod arrays with porous structure under Mg vapor. The structural properties of the Si and Mg2Si nanorods were investigated. The morphology of the Si nanorod arrays is preserved in the Mg2Si nanorod arrays. The diameter and height of the Mg2Si nanorods were significantly increased to 420 nm and 600 nm compared to those of the Si nanorods. The volumetric expansion from Si nanorods to Mg2Si nanorods is about V (Mg2Si) /V-Si=1.55 and the density of Si nanorods with porous structure is about 48.3%. Periodic Mg2Si nanorod arrays will be useful to control thermal and/or solar radiation. (c) 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim