Display omitted •A magnetic bionanocomposite based on carboxymethyl dextrin was fabricated.•Bionanocomposite showed good antibacterial and antioxidant activities and low toxicity.•Bionanocomposite showed good physicochemical properties such as solubility and conductivity.•Bionanocomposite can have good potential applications in biomedical applications. Nowadays, nanocomposites based on carbohydrate polymers owing to good physicochemical and biological properties have found promising applications in various fields especially biomedical applications. In the current study, a bioactive nanocomposite based on carboxymethyl dextrin-grafted-poly(aniline-co-meta-phenylenediamine) and iron oxide/copper oxide (CMD-g-PACPD@Fe3O4/CuO) was prepared by an in-situ copolymerization method. Several analyses such as FT-IR, NMR, EDX, BET, XRD, UV–vis, FE-SEM, TGA, VSM, and DLS were employed for the characterization of prepared materials. The NMR spectroscopy confirmed the preparation of carboxymethyl dextrin. The FTIR and EDX analysis showed that the CMD-g-PACPD@Fe3O4/CuO nanocomposite was prepared successfully. The specific surface area of about 11.30 m2/g was obtained for CMD-g-PACPD@Fe3O4/CuO nanocomposite by using BET analysis. The specific conductivity values of CMD-g-PACPD@Fe3O4/CuO were obtained in a range of 0.3 to 102 µS/cm in various solvents. The solubility test showed that the best solvent for the dispersion of the CMD-g-PACPD@Fe3O4/CuO was dimethyl sulfoxide. A superparamagnetic property of the CMD-g-PACPD@Fe3O4/CuO with saturation magnetism (MS) of 16.49 emu/g was obtained by VSM analysis. The CMD-g-PACPD@Fe3O4/CuO nanocomposite had good antioxidant (54 %) and antibacterial (against Escherichia coli and Staphylococcus aureus) activities and low toxicity at high concentrations (500 mg/mL). The current work may shed light on the potential applications of CMD-g-PACPD@Fe3O4/CuO in biomedical applications.