In this study, the authors presented synthesis of ceria nanoparticles (NPs) by the bio-reduction method and their antioxidative activity. Aqueous extract of Euphorbia (Euphorbia amygdaloides) was used as reducing and stabilising agents. They used aqueous extract of Euphorbia (E. amygdaloides) as reducing and stabilising agent. Ultraviolet-visible (UV-vis) absorption spectroscopy was used to monitor the quantitative formation of ceria NPs. They also addressed the characteristics of the obtained ceria NPs using scanning electron microscopy (SEM), X-ray diffraction (XRD) and transmitting electron microscope (TEM). The synthesised cerium (III) oxide (Ce2O3) NPs were initially noted through visual colour change from colourless pale yellow cerium (III) to light yellow cerium (IV) and further confirmed the band at 345 nm employing UV-vis spectroscopy. The average diameter of the prepared NPs was about 8.6-10.5 nm. In addition, the synthesised Ce2O3 NPs were tested for antioxidant and anti-bacterial activities using ferric reducing antioxidant power, cupric reducing antioxidant capacity, ferrous ions chelating activity, superoxide the anion radical scavenging and 2, 2'-azinobis 3-ethylbenzothiazol to-6-sulphonic acid scavenging activity. It could be concluded that Euphorbia (E. amygdaloides) extract can be used efficiently in the production of potential antioxidant and anti-bacterial Ce2O3 NPs for commercial applications.