This Letter reports the growth of well-aligned carbon nanotubes (CNTs) having increased growth rate at reduced growth temperature as a result of using Fe-Si as the catalyst. Fe-Si catalyst leads to not only a low growth temperature of 370 degreesC but also an unprecedented, rapid growth kinetics. The lengthening of CNTs was found to be proportional to t(15) where t is the growth time. The use of Fe-Si as the catalyst enhances the carbon diffusivity in the catalyst. Due to the enhanced carbon diffusivity and the nonlinear growth kinetics, a reaction-controlled growth model is suggested. (C) 2004 Elsevier B.V. All rights reserved.