Abstract: In this study, we report the synthesis and characterization of pure cerium oxide (CeO₂) and manganese-doped cerium oxide (Mn–CeO₂) nanoparticles using the co-precipitation method. This synthesis route offers a simple and efficient pathway for obtaining high-purity nanomaterials. Structural and optical properties of the synthesized nanoparticles were analysed using X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), and UV-visible diffuse reflectance spectroscopy (UV-DRS). XRD analysis confirmed the formation of crystalline CeO₂ with a fluorite cubic structure, both in pure and Mn-doped samples. The incorporation of Mn did not alter the primary crystal phase but may have induced subtle lattice distortions. FESEM images revealed that the particle size ranges from approximately 10 nm to 40 nm, indicating successful nanoscale synthesis. UV-DRS results demonstrated enhanced visible light absorption in Mn-doped CeO₂ compared to pure CeO₂, suggesting a narrowed bandgap and potential for improved photocatalytic performance. These findings highlight the influence of Mn doping on the structural and optical behaviour of cerium oxide nanoparticles.