Polycarbosilane thin films were deposited using a d.c. plasma process, taking advantage of the high deposition rate and self-healing process of d.c. discharge polymerization on a conductive substrate such as steel. A unique deposition and surface analytical system was designed and constructed to deposit and analyze the polymer films in situ. The steel substrate, exposed to argon and hydrogen plasma, was found to be essentially free of carbon and oxygen. In-situ X-ray photoelectron (XPS) analysis of the initial stage plasma deposition provided evidence of chemical bonding between the steel substrate and plasma-deposited polypolycarbosilane film. An air-ageing test of the plasma polycarbosilane film showed only surface oxidization. However, incorporation of oxygen into the starting gas composition resulted in fully oxygenated polymer films. Film structure and properties were characterized by XPS and Fourier transform infrared spectroscopy.