Oxidative modification of low-density lipoprotein (LDL) is a key initiating event in atherosclerosis. Dietary antioxidants may retard this process. This study evaluated the in-vitro antioxidant activity of an aqueous extract of Allium cepa (onion) and explored its phytoconstituents by in-silico docking against human serum transferrin, a protein implicated in oxidative-stress regulation. Methods: An aqueous bulb extract was assessed for DPPH, hydroxyl and superoxide radicalscavenging activity (10-100 ug/mL) against standards. Isoquercetin glycoside, trigalloyl glucose and cycloalliin were docked into human serum transferrin (PDB 1N7W) using Molegro Virtual Docker, with atorvastatin as the reference. Results: The extract showed concentration-dependent scavenging with IC50 values of 26.84 ug/mL (DPPH), 42.07 ug/mL (hydroxyl) and 50.54 ug/mL (superoxide), weaker than the standards. In docking, isoquercetin glycoside bound most strongly (MolDock - 125.39; rerank -95.48; H-bond -13.13), exceeding atorvastatin (-111.60). Conclusion: Allium cepa extract has appreciable antioxidant activity, and isoquercetin glycoside is a strong transferrin-binding phytoconstituent, supporting the antiatherosclerotic potential of onion through antioxidant and molecular mechanisms