Cerium oxide (CeO2) and 1%, 5% and 10% tin-doped CeO2 nanoparticles (Sn-doped CeO2 NPs) were synthesized using aqueous leaf extracts of Pometia pinnata. UV-Vis diffuse reflectance spectroscopy showed band gap energies of 2.47-2.66 eV. X-ray diffraction results confirmed the formation of a fluorite phase of CeO2 and Sn-doped CeO2 NPs with average crystallite sizes between 6 and 19 nm. X-ray photoelectron spectroscopy (XPS) analysis further established the synthesis of CeO2 and Sn-doped CeO2 NPs. The density of states was proposed accordingly using the valence band-XPS data. Scanning electron microscopic and transmission electron microscopic studies showed almost spherical shaped particles with average particle sizes around 15-20 nm. All synthesized nanomaterials were tested for photoantioxidant activity under visible light and in the dark and showed improved photoantioxidant activity under visible light irradiation for dose and time-dependent studies. The synthesized nanomaterials were also tested for antibiofilm activities and exhibited significant concentration-dependent antibiofilm activity against Gram-positive pathogenic bacteria such as Staphylococcus aureus and Listeria monocytogenes. The 10% Sn-doped CeO2 NPs and S-CeO2 NPs also exhibited bactericidal activity against Staphylococcus aureus. These studies showed that S-CeO2 and Sn-doped CeO2 NPs have both good antioxidant and antibacterial properties. This journal is