Outwardly oriented leaf-like gallium nitride crystal assemblies were synthesized on alumina substrate by a facile thermal chemical vapor deposition method. The as-grown products were spherical conglomerate with "leaves" radiating from central core distributed sparsely on substrate. Each "leaf' with flat and smooth surface was single crystalline GaN with hexagonal structure, its normal dimensions were 4 mu m in thickness, 35 mu m in width and 300 gm in length. The micro-Raman measurement had shown E-2(high) mode located at 567cm(-1) with a FWHM of 4cm(-1) as well as the room temperature photoluminescence result of a strong near-band-edge emission at 369 nm without the yellow band evidenced the good crystalline quality of as-prepared "leaf"-like GaN crystal. The formation mechanism of leaf-like crystal assemblies was systematically investigated and discussed on the basis of the experiment results. The resultant leaf-like crystal assembly may be a promising building block for three-dimension device applications in future. (c) 2006 Elsevier B.V. All rights reserved.