This study aimed to prepare a corn straw-derived biochar supported nZVI magnetic composite (nZVI/BC) and evaluate its efficiency in adsorption of malachite green dye (MG). The prepared nZVI/BC composite was characterized by XRD, FTIR, TEM, TEM-EDS, VSM, XPS, TGA, zeta potential and BET surface area. The prepared mesoporous composite showed enhanced efficiency for the adsorption of MG dye. Adsorption models and kinetic results indicated that the adsorption of MG onto nZVI/BC composite was more fitted to Langmuir isotherm and follows second order kinetics. Intraparticle diffusion model indicated that the adsorption follows a three steps mechanism. The maximum adsorption capacity of nZVI/BC composite (515.77 mg MG/g composite) was much higher than most of reported biochar adsorbents. The removal process of MG onto nZVI/BC composite does not only proceed via adsorption mechanism, but also through an oxidative degradation mechanism. The Magnetic character of the biochar enables its easy separation and reuse for many cycles. (C) 2020 The Society of Powder Technology Japan. Published by Elsevier B.V.