Vertical-aligned Pt nanorods are fabricated on the surface of nanoporous anodic aluminum oxide (AAO) templates by magnetron sputtering. The size effect of AAO templates, which is focused on in this study, would influence the morphology of stacked atoms. The rim of the pores, which act as obstacles to the stacked atoms, could prevent them from forming continuous films. The continuous films are commonly formed because of the larger interpore distance which is compared to the grain size of stacked atoms. Between closely-distributed pores, the shorter interpore distance, namely smaller surface area, indicates insufficient surface energy for heterogeneous nucleation, restricts the growth of stacked atoms. Nevertheless, there still remain regions with larger interpore distance. On these constricted regions, instead of continuous films, isolated nanorods are formed. In this study, a nanorod growth diagram is deduced, and understanding of the growth of nanorods on AAO templates is furthered. (C) 2008 Elsevier B.V. All rights reserved.