A polybithiophene-carbon (PBT/C) composite was synthesized by ball-milling chemically polymerized polybithiophene with carbon nanofibers and found to have n-type redox properties with exceptional reversible capacity and cycling stability. The experimental results demonstrated that the as-synthesized (PBT/C) composite can realize a total two-electron redox capacity of ∼850mAhg−1 with half of the capacity delivered at a low potential plateau of 1.25V in Li+ electrolyte, possibly serving as a high capacity organic anode for Li-ion batteries. More significantly, the PBT/C composite can also be cycled in Na+-electrolyte, delivering a reversible redox capacity of ∼500mAhg−1 through the doping–dedoping reactions of Na+ ions into/from the polymer chains. These n-type redox performances suggest a possible application of the polymers of this type as high capacity and cycling-stable anodes for Li-ion and Na-ion batteries.