Abstract: A CNF/Si composite was synthesized in situ by growing carbon nanofibers on the surface of silicon particles through catalytic chemical vapor deposition. Microstructures of the composites were characterized by scanning and transmission electron microscopy, and X-ray diffraction. Electrochemical measurements indicated that the composite showed higher reversible capacity (1042mAh/g) and better cyclability than did a CNF-Si mixture prepared by simple mechanical milling. A structural evolution mechanism is proposed to explain the superior electrochemical performance of the CNF/Si composite electrode in comparison with the CNF-Si mixture. Scanning electron microscopy and ac impedance analysis indicated that the electrochemical performance can be attributed to the good contact of the in situ grown carbon fiber with the silicon particles.