Networked rectangular MgO nanostructures have been prepared through direct reaction of Mg with flowing oxygen. The nanostructures consist of the branches that have square cross sections and grow in a right-angled zigzag manner to elongate in three dimensions, which form the networked rectangular nanostructures. The edge dimension of their cross-sections is in the range of 50-150 nm. A growth mechanism based on the vapor-solid process is proposed for the formation of the networked nanostructures. (C) 2004 Elsevier B.V. All rights reserved.