In situ growth of ZnO nanobelt arrays from and on zinc substrates (foils and microparticles) has been accomplished by controlled thermal oxidation in the presence of oxygen. The nanobelts grow approximately perpendicular to the Zn substrate surface along the (1120) direction of ZnO, which has a thickness of similar to 3-4 nm, a width tapering from about 50 to 300 nm, and a length of similar to 10-20 mu m. On the basis of the structural analysis and kinetic studies, a tip-growth mechanism is proposed, which underlines the transport of Zn from the substrate to the growing tip. The ratio of UV to green photoluminescent emissions of the as-synthesized ZnO nanobelt arrays could be controlled by varying the reaction conditions. Sharp UV stimulated emission peak is also observed at moderate threshold excitation intensity (similar to 0.7 mJ/cm(2)) showing the high quality of the ZnO nanobelts. The ZnO nanobelts array has also been tested for sensing NH3 gas, and high sensitivity, reversibility, and rapid response have been demonstrated.