Abstract: The growth of carbon nanotubes on the surface of carbon fibers by chemical vapor deposition was investigated and their microstructure was studied by scanning electron microscopy. Results show that grooves on the surface of carbon fibers, which can load catalysts, are locations for the growth of the nanotubes. Cobalt is the best catalyst among Fe, Co, and Ni. Carbon nanotubes are of large diameter when the catalyst concentration is high. Carbon nanotubes cannot be distributed evenly on the whole surface when the concentration of catalysts is low. The optimum catalyst concentration of cobalt nitrate is 0.05mol/L.