Cerium oxide (CeO2) nanoparticles were successfully synthesized by the hydrothermal method with different reaction times. The synthesized CeO2 nanoparticles were characterized by Powder X-Ray diffraction (XRD), Scanning Electron Microscopy (SEM), UV-Vis spectroscopy and FTIR spectroscopy. The effects of the reaction time on the structure and morphology of the prepared samples were investigated using XRD and SEM. The XRD studies reveal that the ceria nanoparticles have face-centered cubic structure. The SEM images reveal that the prepared Ceria nanoparticles are an aggregated form of spherical nanoparticles and the particle size decreases with increasing reaction time. FTIR analysis confirms the presence of CeO2 in the prepared samples. UV-Vis spectral studies show that the UV cut off wavelength decreases and the optical band gap increases with increased reaction time. Photoluminescence (PL) studies indicate that the PL emission of both the samples occurs at 683 nm, however, the emission intensity increases with longer reaction times.