In this paper, the impacts of catalytic particle size on the overall reactor performance for carbon nanotubes (CNTs) production using a fluidized-bed chemical vapor deposition (FBCVD) process have been studied. Six different particle size fractions (10-20 mu m, 20-53 mu m, 53-75 mu m, 75-100 mu m, 100-200 mu m, and 200-300 mu m) were selected. It was observed that the smaller the catalytic particle diameter, the greater the carbon deposition efficiency and the greater CNT synthesis selectivity. The 10-20 mu m catalytic particles exhibited 30% higher carbon deposition efficiency than the 200-300 mu m catalytic particles. The selectivity toward CNTs formation was also approximately 100%. These observations could be explained by the fact that when the diameter of the catalytic particle gets smaller, the breakthrough capacities during frontal diffusion will be bigger due to a shorter diffusion path length within the particle. Moreover, the fine particles ensured high interstitial velocity which subsequently enhances the heat and mass transfer, and consequently improves the CVD reaction. (C) 2010 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.