Magnetic carbon-iron nanoadsorbents fabricated by carbonizing cellulose and reducing Fe3O4 nanoparticles or Fe(NO3)3 (the products are denoted as MC-O and MC-N, respectively) have demonstrated great Cr(vi) removal. MC-N with a higher proportion of zero-valence iron (ZVI) and bigger specific surface area exhibited better resistance to oxygen and acid than MC-O due to its smaller pore size. The Cr(vi) removal was highly pH-dependent. For example, 4.0 mg L-1 Cr(vi) neutral solution was completely purified by 2.5 g L-1 MC-O and MC-N within 10 min. 1000 mg L-1 Cr(vi) solution at pH 1.0 was completely removed by both nanoadsorbents in 10 min. The MC-O nanoadsorbents had a higher removal percentage (98.1%) than MC-N (93.5%) at pH 7.0, while MC-N had a removal capacity of 327.5 mg g-1, much higher than 293.8 mg g-1 of MC-O at pH 1.0. A chemical adsorption was revealed from the pseudo-second-order kinetic study. Monolayer adsorption of Cr(vi) was revealed by a better fitting of the Langmuir model isotherm, rather than multilayer adsorption for the Freundlich model. These nanoadsorbents could be easily separated from solution by using a permanent magnet after being treated with Cr(vi). Finally, the Cr(vi) removal mechanisms were proposed considering the Cr(vi) reduction and precipitation of Cr(iii).