The densification of carbon fiber substrates by chemical vapor deposition (CVD) is a process quite used since the fifties, for manufacturing carbon reinforced with carbon fiber composites (CRCF). The process is based in thermal decomposition of a gas which contains carbon in its molecules and the resulting pyrolytic carbon is continually deposited onto de carbon fiber substrate. For this experiment the substrate material was made of carbon fiber felt. The deposition was performed by isothermal process at atmospheric pressure and at temperature of 1050 oC. Methane (CH4) gas was used as carbon bearer and nitrogen (N2) as the carrier gas. Different volumetric ratio of N2 and CH4 (N2:CH4) were used in order to get an optimum densification of the substrate. Optical and electron scanning microscopy and density measurements were used to characterize the impregnated material. An increase in ratio of N2 and CH4 increase the overall deposition for the same time interval.