Abstract: A Fe2O3/Al2O3 binary aerogel was used as a catalyst for the synthesis of singlewalled carbon nanotubes (SWCNTs) by the catalytic decomposition of CH4H2 and a CH4H2water mixture at 900℃ for 3min. The influence of water vapor on the growth of SWCNTs was investigated by characterizing the morphology and structure of the carbon products using scanning electron microscopy, Xray diffraction, transmission electron microscopy, and Raman spectroscopy. Results show that SWCNTs with a high purity were synthesized under the mixed atmosphere of CH4H2water when the amount of water vapor present was controlled by bubbling H2 through water. The yield and microstructure of the asformed carbon products can be correlated with the composition of the reaction mixture.