Nanocrystals of zinc oxides have demonstrated to be very important materials for several applications in many fields, particularly in catalysis. Nanocrystalline zinc peroxide (ZnO2), which is a precursor of zinc oxide (ZnO), has been prepared by means of a hydrothermal process from zinc acetate dehydrates. On the other hand, it is of great interest to have a detailed structural characterization, in order to correlate it with the catalytic properties of the synthesized material. In this work, some results are presented about the nanostructure of the prepared zinc peroxide. By using X-ray diffraction followed of a pattern refinement by the Rietveld techniques, refined average cell parameters and crystallite size were calculated and, from these refined values, crystallite morphology was simulated in an averaged manner. With the aim to get a more complete characterization, besides these results, some micrographs of the crystalline structure of ZnO2, observed by TEM, were also included in this work.