Single crystalline ZnO nanowires were grown using standard hydrothermal growth process and subsequently closed nanopores were obtained by post-annealing in various conditions. The pore size, shape and spatial distribution are studied with various temperatures, time and gas (Ar and H-2) mixture combinations during the annealing. The annealing treatment with Ar only at elevated temperatures seems to produce more thermodynamically stable closed pores. From the thermodynamically equilibrium pores with average size of 12 nm, the surface free energy of ZnO{10-13} is determined as similar to 0.99 Jm(-2) experimentally by "inverse Wulff's construction". (C) 2011 The Electrochemical Society. [DOI: 10.1149/2.014203jes] All rights reserved.