Carbon nanotubes (CNTs) were synthesized by the catalytic decomposition of acetylene over nanosized metallic iron. A high metal loading was chosen in order to obtain a longer catalytic activity. Different nanosized iron oxides were prepared using chemical methods. A catalyst of the composition 40% Fe2O3:60% Al2O3 is prepared by wet impregnation method. The prepared samples of iron oxides supported in alumina were completely reduced by hydrogen gas at 500 degrees C and then constant rate of acetylene gas was passed over the freshly reduced samples at different reaction conditions. The kinetics of CNTs synthesis on reduced nanosized Fe2O3 supported on alumina was investigated as a function of crystal size of iron oxide catalyst (35-150 nm) and decomposition temperature (400-700 degrees C). The microstructure and morphology of the synthesized catalyst and CNTs were characterized using scanning electron microscope (SEM), high-resolution transmission electron microscope (HR-TEM) and XRD analysis. The results revealed that both the crystal size of iron oxide and decomposition temperature have a significant effect on the percentage yield of carbon deposited. It increased by decreasing crystal size of the catalyst and increasing decomposition temperature to certain limit. The maximum yield of carbon deposited (426%) was obtained at decomposition temperature 600 degrees C and over nanosized iron oxide catalyst with crystal size of average 35 nm. (C) 2008 Elsevier B. V. All rights reserved.