Cerium oxide (CeO2) nanostructures were synthesized using an ozonolysis assisted co-precipitation method, while varying the ozonolysis reaction times for 1, 2, 3 and 4 h in the systems. The effect of ozonolysis reaction time on the morphology and optical properties of CeO2 was investigated. The resulting products were characterized using X-ray diffraction (XRD), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), ultraviolet-visible spectroscopy (UV-Vis), photoluminescence spectroscopy (PL) and BET surface area analysis. The XRD patterns confirm a face-centered cubic (FCC) CeO2 having crystalline sizes ranging from 8.5 to 10 nm. From the TEM images, longer ozonolysis reaction times more completely transform the morphology of CeO2 nanoparticles from a nanocube-like shape into hexagonalCeO(2) nanostructures. FTIR spectra show that the peaks in the region of 400-750 cm(-1) are due to CeO2 stretching vibrations. The UV-Vis spectra of all samples show strong absorption at 285 nm with a weak absorption peak around 360 nm. The band gap energy is independent of ozonolysis reaction time. The photoluminescence spectra show characteristics peaks of CeO(2 )nanoparticles. Adsorption-desorption isotherms of CeO2 show a typical IUPAC type IV pattern and their pore size is 3.28 nm.