ABSTRACT The multiwall carbon nanotubes modified by iron–manganese binary oxide (FeMnOx/MWCNTs) were successfully synthesized followed a chemical co-precipitation method. The FeMnOx/MWCNTs showed superior adsorbability to Cr(VI) and As(III) in aqueous solution. The physicochemical property of materials was discussed by various characterization methods including SEM, EDS, BET, XRD, XPS, Raman, and FTIR analysis. The effect of different reaction conditions on Cr(VI) and As(III) adsorption, including pH, ionic strength, adsorbent dosage, and initial concentration, was studied. In a single system, the maximum adsorption capacity of Cr (VI) and As (III) on FeMnOx/MWCNTs was, respectively, 47.25 mg/g at pH 2.0 and 31.11 mg/g at pH 4.0, and the adsorption of both Cr(VI) and As(III) better fitted with Langmuir isotherm and pseudo-second-order kinetic models. In the binary system, the EFMI model described the adsorption process of Cr(VI) and As(III) better. The electrostatic attraction played the main role in the adsorption of Cr(VI), while the redox and ligand exchange could be responsible for the adsorption of As(III). It was found that the redox transformation occurred between As(III) and Cr(VI) after the two contaminants were co-adsorbed onto the surface of FeMnOx/MWCNTs. The desorption-resorption studies showed the FeMnOx/MWCNTs had good reproducibility and recycling performance.