Radionuclide contamination has become an urgent problem with the development of nuclear power plants. Herein, chemical-decorated core-shell magnetic manganese dioxide (denoted as Fe3O4@C@MnO2) composites were synthesized via transforming KMnO4 to MnO2 on the carbon-covered magnetite (Fe3O4@C) microsphere surface. It was employed to remove U(VI) and Eu(III) ions from aqueous solution under various conditions. The kinetic adsorption data were well simulated by the pseudo-second-order model and adsorption isotherms were fitted well by Langmuir model. Moreover, the maximum uptake capacities were up to 77.71 mg/g for U(VI) and 51.01 mg/g for Eu(III) at pH = 5.0 and T = 298 K. Adsorption behavior was strongly related to pH values but weakly affected by ionic strength, implying that the interaction of U(VI)/Eu(III) with Fe3O4@C@MnO2 was mainly dominated by inner-sphere surface complexation. XPS analysis illustrated that the interaction of Eu(III)/U(VI) with Fe3O4@C@MnO2 was associated with the strong metal bonds (MnO), hydroxyl bonded on metal (Mn-OH) and carboxyl groups (-COOH) by surface complexation and zeta potential results implied that the adsorption process was governed by electrostatic attraction. This research highlighted the outstanding performance of Fe3O4@C@MnO2 in eliminating Eu(III)/U(VI) ions from aqueous solutions, which was of great significance in the future application in radionuclides' pollution treatment.