Herein, we developed an efficient method for covalent functionalization of reduced graphene oxide (rGO) with imidazolium-based poly(ionic liquid)s via the Diels-Alder (DA) click reaction in deep eutectic solvents (DESs). Firstly, poly(ionic liquid)s (P(F-IL)s) containing furfuryl and imidazolium were prepared by the reaction of poly(chloromethylstyrene-co-maleicanhydride), furfuryl amine and methylimidazole. Afterward, the P(F-IL)s were grafted directly on the rGO surface via the DA reaction in a deep eutectic solvent (DES) without catalyst under ultrasonication. The obtained hybrid materials were characterized by FT-IR, TGA, Raman spectroscopy, XPS, SEM, and TEM. The capacitive and electrochemical behaviors of the hybrid materials were studied by using cyclic voltammetry (CV) and electro chemical impedance spectroscopy (EIS). In CV, the rGO-P(F-IL) hybrid showed the largest capacitance and EIS revealed a lower diffusion resistance compared to that of rGO, which indicated a good electrochemical capacitor behavior of the hybrid. © 2020 Elsevier B.V.