Recently, biosynthesis of nanoparticles (NPs) using plants extract have been received considerable attention owing to production of biocompatible and water-soluble NPs. In addition to that, low cost, freely availability, generally less toxicity and stability properties of plant extracts have made them heavily use in synthesis of various types of NPs. In synthesis strategy, some components in plant extract act as reducing and/or even capping agents for formation and stabilizing of NPs. In this current study, we report the biosynthesis of stable iron oxide (Fe3O4) NPs using anthocyanin rich-red cabbage extract (RCE) (Brassica oleracea var. capitata) with their antimicrobial and antioxidant properties. The potential mechanism for synthesis of the Fe3O4 NPs is as considered: i) occurrence of iron ions (Fe2+)?anthocyanin complexes, ii) oxidation of hydroxyls on the aromatic groups of anthocyanins, ii) reduction of Fe2+ and iv) formation of the Fe3O4 NPs. We demonstrated that the Fe3O4 NPs showed greater stability with enhanced antimicrobial and antioxidant properties. The magnetic feature of the Fe3O4 NPs provided two benefits. Firstly, the Fe3O4 NPs were collected from reaction media without centrifugation using an external magnet and secondly, the magnetic feature also allows us for repeated use of the Fe3O4 NPs in antioxidant applications.