In the previous study, authors have showed the outstanding material properties of Ce4+ doped ZnO (Zn/x%Ce) nanoparticles, which were successfully synthesized by hydrothermal and ultrasonic assistedmethod. In this research, authors continue to investigate the optical characteristics, band gap energy of Zn/x%Ce nanoparticles and application to treatment of rhodamine B (RhB) in water. The PL spectrum of the Zr/5%Ce material has a peak at 420 nm, corresponding to the process of electron transfer from the 5d orbitals to the 4f orbitals of Ce4+. The broad overlapping emission band in the fluorescence spectrum is due to the contribution of Ce3+ ions. The Ce4+ and Ce3+ ions replaced Zn2+ ions, significantly reducing the bandedge emission of ZnO at 385 nm. Based on the diffuse reflectance spectra, band gap energies of Zn/x%Ce nanocomposites are determined about 2.99-3.14 eV and the energy absorption in the visible region. Rhodamine B was partially adsorbed by Zn/x%Ce nanoparticles with an efficiency of 10.435-20.676%. According to Lagergren's second-order adsorption kinetics equations for RhB with the correlation coefficient R2 = (0.9835-0.9921) closed to 1. Notably, the Zn/x%Ce nanoparticles have good photocatalytic ability, the photodegradation efficiency of 92.665% is calculated for RhB when irradiated visible light in 3 hours. The photodegradation reaction according to the 1st order decomposition reaction kinetics model. Based on outstanding properties, the Zn/x%Ce nanoparticles are potential use in the treatment of organic dyes in wastewater is very promising.