In this study, we report the synthesis and comprehensive characterization of pure Yb₂O₃, pure CeO₂, and mixed Yb₂O₃:CeO₂ nanoparticles with varying molar ratios, prepared via a simple sol-gel method followed by thermal treatment. Structural analysis by X-ray diffraction (XRD) confirmed the formation of cubic crystalline phases for all samples, with crystallite sizes ranging from 24.5 nm for pure Yb₂O₃ to 5.1 nm for the 1.0Yb₂O₃:0.5CeO₂ composition, indicating that Ce incorporation leads to significant crystallite size reduction. The addition of CeO₂ induced lattice strain and increased dislocation density, reflecting the presence of structural distortions and enhanced defect formation, which suggest the successful incorporation of Ce ions into the Yb₂O₃ matrix and the formation of solid solutions. X-ray photoelectron spectroscopy (XPS) analysis confirmed the chemical composition and oxidation states of the constituent elements. The O 1 s spectra revealed contributions from lattice oxygen and oxygen vacancies, indicating defect-related features that may influence the electronic properties. The Ce 3d spectra displayed a dominant Ce4+ component with the presence of Ce3+ species, implying partial reduction, redox activity, and the potential for oxygen storage or catalytic applications. Yb 4d spectra confirmed the presence of Yb3+ without evidence of Yb2+ species. The experimental atomic ratios closely matched the theoretical stoichiometries, validating the compositional homogeneity and stability of the synthesized nanomaterials. Overall, the synthesized Yb₂O₃:CeO₂ nanomaterials exhibit tunable structural, electronic, and defect properties, making them promising candidates for applications in catalysis, gas sensing, and energy-related devices, where defect engineering and redox activity are critical for enhancing performance.