This study reports the synthesis of CeO<inf>2</inf>/ZrO<inf>2</inf> nanocomposite via the biogenic route utilizing Citrus limonium (lemon juice) along with the CeO<inf>2</inf> and ZrO<inf>2</inf> nanoparticles for comparative purposes. The XRD analysis confirms the effectual formation of phase-pure and good crystalline CeO<inf>2</inf>/ZrO<inf>2</inf> nanocomposite, exhibiting a mixed cubic and tetragonal structure with an average crystallite size of 66 nm. FT-IR analysis exposes the characteristic metal-oxygen bonds along with organic functional moieties. The UV-visible diffuse reflectance results show strong absorption from 200 to 420 nm for the CeO<inf>2</inf>/ZrO<inf>2</inf> nanocomposite, with a bandgap of 3.22 eV. The surface morphology of the nanocomposite reveals a foundation of irregular, block-like ZrO<inf>2</inf> structures, with affixed smaller aggregates of CeO<inf>2</inf> on the ZrO<inf>2</inf> surface with interstices between them. Furthermore, the co-occurrence of Ce3+ and Ce4+ oxidation states, along with Zr4+ and surface oxygen species, significantly boosts the nanocomposite's redox activity. Antibacterial assays demonstrated that the CeO<inf>2</inf>/ZrO<inf>2</inf> nanocomposite exhibited the highest inhibition zones in Salmonella typhi and Bacillus subtilis, surpassing individual nanoparticles. Antioxidant studies show 83% DPPH radical scavenging activity and 88% superoxide anion free radical scavenging activity. The antidiabetic activity study shows 89% inhibition of α-amylase and 86% inhibition of α-glucosidase at 950 μg/mL, which is better than the individual nanoparticles. This insightful study emphasizes the compelling potential of CeO<inf>2</inf>/ZrO<inf>2</inf> nanocomposite for advancing therapeutic strategies and significantly improving clinical outcomes across a range of medical conditions. © 2025 Elsevier B.V., All rights reserved.