A polyimide–MWCNT composite (PNP@CNT) synthesized from 1,4,5,8-naphthalenetetracarboxylic-dianhydride (NTCDA) and phenylene diamine (PDA) was investigated as a novel anode for aqueous Na-ion batteries. This composite demonstrates a high reversible capacity of 149 mA h g⁻¹ at quite a low potential of −0.65 V (vs. SCE), superior rate capability and long-term cycling stability. The feasibility of PNP@CNTs in aqueous Na-ion full batteries is also confirmed in conjunction with the Na_0.44MnO₂ cathode, possibly serving as a high performance aqueous Na host anode for large-scale electric energy storage applications.