Methane and fluoromethanes (CHnF4-n, 1 less than or equal to n less than or equal to 3) were subjected to an rf glow discharge plasma. All the fluoromethanes (including methane) polymerized in the plasma and formed thin films. The deposition rate of the fluoromethanes depended on their monomer structure : CH2F2, of which the F/H ratio is unity, showed the greatest deposition rate. The elimination of H and F atoms as H-F was found to be a key factor for the polymerization of fluoromethanes. The chemical composition of the polymerized film, measured with X-ray photoelectron spectroscopy and glow discharge emission spectroscopy, was also found to be strongly dependent on monomer structure.