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 similar to 850 mAh g(-1) with half of the capacity delivered at a low potential plateau of 1.25 V 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 similar to 500 mAh g(-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. (C) 2012 Elsevier Ltd. All rights reserved.