A variety of techniques have been applied for 40 years in order to characterise Ziegler-Natta catalysts, however, few studies report the use of surface science technologies in an effort to understand surface structure, composition and chemical bonding in MgCl2 supported catalytic system. In this paper, the synthesis and the characterisation of the MgCl2/TiCl4/AlEt3 catalyst in controlled conditions is reported. Our aim is to understand (1) the activation process of the magnesium chloride support: (2) the interaction between the magnesium chloride support and TiCl4; (3) the chemical structure of the titanium active centres formed by treatment of the procatalyst, MgCl2/TiCl4, with the co-catalyst, TEA (triethylaluminium); (4) which Tin+. species is active in ethene and propene polymerisations. These experiments were performed in conditions as similar, as possible, to the ones used for laboratory synthesis and polymerisation. The experiment consists of different steps: (1) preparation of delta-MgCl2 under strictly inert atmosphere as previously reported [1]; (2) activation of delta-MgCl2 in a UHV chamber by means of argon ion sputtering; (3) exposure to TiCl4 vapours: (4) exposure to TEA. The surface composition was checked during the experimental steps by means of XPS technique. (C) 2002 Elsevier Science B.V. All rights reserved.