A series of polyaniline-LiFePO4 (PAn-LiFePO4) composites were synthesized by in situ polymerization. The samples were characterized by thermogravimetry (TG) and scanning electron microscope (SEM). Electrochemical impedance measurements showed that the polyaniline significantly decreased the charge-transfer resistance of LiFePO4 electrodes. Charge–discharge properties of composites as cathode materials for lithium-ion batteries were studied. The results indicated that PAn-LiFePO4 composites had higher discharge capacity and better cycling property. The PAn-LiFePO4 composite with 25 wt% polyaniline showed the best electrochemical performance. Its first specific discharge capacity was 140.3 mAh/g at 0.1 C and its specific discharge capacity was 118.7 mAh/g after 50 cycles at 1 C. Copyright © 2009 John Wiley & Sons, Ltd.