We investigate high aspect ratio ZnO nanorods during Li-battery cycling by stepwise characterization of their crystal structures and porosities. During the cycling, nonporous ZnO nanorods become porous and, as a result, the surface area of ZnO nanorods increases significantly. As the Li amount inserted and extracted increases, it was observed that nanopores progress from the surfaces to the cores of ZnO nanorods. Also, in the crystal structure viewpoint, the original single-crystalline structure of the pristine ZnO nanorods gradually turns into the polycrystalline during the pore progression. This investigation not only delivers detailed information on the morphology and crystal structures of one-dimensional ZnO nanostructures during the course of Li-battery operations, but also suggests that battery processes can be a useful means to manipulate the crystal structure and porosity of ZnO nanostructures. (C) 2012 The Electrochemical Society. [DOI: 10.1149/2.020301jes] All rights reserved.