Zinc oxide (ZnO) and Zinc peroxide (ZnO2) nanoparticles were synthesized by colloidal method at low temperature. The thermal stability of ZnO2 was studied by thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and X-Ray diffraction (XRD). The crystalline structure and phase change from ZnO2 to ZnO by heat treatment was studied in detail. Morphology and particle size was examined using Transmission Electron Microscopy (TEM), for as synthesized ZnO and ZnO2 the shape of particles were cuasi-spherical for both materials with average size of 10±2.2 nm and 2.5±0.4 nm, respectively; The crystal size for ZnO obtained by heat treatment was 8±2.2 nm. Electron density contours show the chemical bond type ionic and covalent for ZnO and ZnO2. The vibrational properties were analyzed by Raman and IR spectroscopy. Band gap values were obtained from ultraviolet-visible (UV-Vis) absorbance spectrum. Photoluminescence (PL) spectrum for ZnO shows two emission edges located at 445 and 492 nm and in the case of ZnO2 presents one edge at 364 nm originated from the band edge emission. The optical spectra present a hypsochromic shift, compared with some reported in the literature.