Ordered nanostructure of single-crystalline GaN nanowires in a honeycomb structure of anodic alumina was synthesized through a gas reaction of Ga2O vapor with a constant ammonia atmosphere at 1273 K in the presence of nano-sized metallic indium catalysis. Atomic force microscopy, x-ray diffraction, Raman backscattering spectroscopy, scanning electron microscopy, and transmission electron microscopy indicate that the ordered nanostructure consists of single-crystalline hexagonal wurtzite GaN nanowires in the uniform pores of anodic alumina about 20 nm in diameter and 40–50 μm in length. The growth mechanism of the ordered nanostructure is discussed. The photoluminescence spectrum of this nanostructure is also reported.