Large-scale ZnO hollow spheres were fabricated by a novel in-situ gas growth method. The key strategy for the successful realization was that we employed a high concentration of H2O2 in the preparation procedure. The whole process was carried out under hydrothermal condition without any assistance of surfactant. The O-2 bubbles, originating from the in-situ decomposition of H2O2, served as a soft template. The morphology, structure, composition and catalytic activity of the product have been investigated with XRD, SEM, TEM and TG-DSC. In order to demonstrate the important roles of reactive temperature, H2O2 and urea concentration, a series of controlled experiments have been carried out. It was worth noting that hexagonal wurtzite ZnO made up of various ZnO single-crystal nanosheets could be obtained, when we changed the concentration of urea to 0.4 M. In addition, the fabrication mechanism of ZnO hollow microspheres was discussed in detail. Moreover, the product showed high effective catalytic activity on the decomposition of ammonium perchlorate. (C) 2012 Elsevier B.V. All rights reserved.