Carbon nanowall films prepared on the stainless steel substrates by hot-wire chemical vapor deposition using CH4 with different hydrogen dilution ratios and structure variation in the CNWs against hydrogen dilution have been studied, In the scanning electron microscope image, the wall height and width in the samples prepared with the hydrogen dilution ratio, H-2/CH4+H-2), between 10% and 25% were larger than that prepared without hydrogen dilution. In the Raman spectra for the samples prepared with the H-2/(CH4+H-2) below 25%, the intensity ratio of the G peak to the D peak, I-G/I-D, increased with increasing the H-2/(CH4+H-2). In the samples prepared with the H-2/(CH4+H-2) over 25%, the wall size and the I-G/I-D decreased. (c) 2007 Elsevier B.V. All rights reserved.