This work brings a thorough investigation of hydrothermally derived ceria nanoparticles doped with copper in a wide range of concentrations: CuxCe1-xO2, where x = 0, 0.1, 0.2, 0.3, 0.4, and 0.5, respectively. X-ray diffraction (XRD) analysis showed no additional phases for all samples up to x = 0.4, which exceeds the maximum amount of copper incorporated into ceria without the appearance of copper oxide phase reported in the literature. However, the inductively coupled plasma mass spectrometry (ICP-MS) and energy-dispersive X-ray spectroscopy (EDS) analyses showed that copper is incorporated into the ceria crystal lattice in amounts far lower than the nominal. Nevertheless, the addition of copper has a significant influence on the ceria properties. The size of the obtained nanoparticles was determined by transmission electron microscopy (TEM) and it decreases with the increase of the copper amount from 6 nm for the pure sample to 3.8 nm for the 40 mol. % Cu-doped CeO2 sample. In accordance with the small particle size, the specific surface area, determined from nitrogen adsorption–desorption isotherms at 77 K, is in the range of 196 to 222 m2 g−1. The increase in the copper amount also causes the reduction of the band gap, as determined by UV–Vis reflectance analysis (UV–Vis DRS), and an increase of reducibility, as proven by temperature-programmed reduction by hydrogen (H2-TPR).