To investigate the catalytic mechanism for the growth of carbon nanotubes (CNTs), carbon materials was synthesized at 680°C with a gas mixture of CO-H2 after reduction at 800°C by H2 gas. The synthesized carbon materials on reduced metallic surface were comprehensively explored by scanning electron microscopy (SEM) and X-ray diffraction patterns (XRD) at various reaction times of 2, 10, 70, and 150 min, respectively. The carbon materials synthesized by metal Pt were little affected by reaction time, and only the sintered particles were observed without formation of CNTs. From X-ray analysis, iron oxides synthesized for 2 min were completely converted to iron carbide (Fe3C) without Fe peaks. After 5 min, iron carbide (Fe3C) and carbon (C) phases were observed at the beginning of CNTs growth. It was found that the intensity of carbon(C) peak was gradually increased with the continuous growth of CNTs as reaction time increases. The carbon materials synthesized from the metal Pt were amorphous. It was also found that a catalyst on growth of CNTs was metal carbide.