The development of a deposition system based on DC plasma-assisted chemical vapour deposition (T. Le Huu, H. Nery, H. Zaidi and D. Paulmier, Diamond Relat. Mater., 3 (1994) 1028-1033) has great interest for vapour deposition processes. This process permits the deposition on steel or on glass and other substrates. The advantages of the process are him uniformity on very large surfaces and good adhesion. Diamond and diamond-like carbon were deposited from the plasma with an acetylene-hydrogen mixture (C2H2-H-2). The surface properties and the structure of the films were controlled. The friction and wear behaviour of the film was recorded and analysed. Using scanning electron microscopy and electron energy loss spectroscopy we have shown that the transformation of sp(3) to sp(2) carbon sites occurs on the rubbing surface during friction. This transition will be discussed in connection with the flash temperature created at contact asperities. Transition temperature will be calculated as function of Hertzian contact pressure. The aim of this paper is to present the wear and friction behaviour of diamond like carbon films in vacuum or under water vapour and to study the phase transformation of sp(3) to sp(2) bonds in different gaseous environment surrounding the tribe-contact.