During the process of growth and exploitation of films can occur the strong internal tensions that after relaxation may cause its defo1mation and destruction. Thin films - means the existence of a substrate of other materials with prope1ties differing from film material. Therefore mechanical properties of thin films depend also on the features of substr·ate [I]. In this paper we studied the mechanical prope1ties of Cu thin films grown on MgO ( 4) substrate. The Cu films were obtained by the method of magnetron sputtering (with Magnetron Sputtering RF) at room temperature with thickness t=85 (I), 470 (2), 1000 (3) nm. The roughness, Ra, of the surface of thin films was estimated using the atomic force microscope and optical microscopes. The results are shown in Table I. Nanoindentation was canied out on the Nanotester-PMT-3-NI-02 using the dynamical regime of penetration. The loads on the Berkovich indenter varied in the limits Pmax=2+900 mN. For the calculation of the Young elastic modulus (E) and hardness (H) of the thin films was used the method proposed by Oliver-Phan (2]. The H and E values were evaluated as the mean of five indentations applied at the same load. Fig. I shows the dependences of Hand E as a function of applied load. From the data above we see that the roughness Ra decreases with increase of film thickness (Table I). Hardness and Young's modulus of the Cu/MgO composed structure also depends on film thickness, these parameter values decrease with increase of the film thickness (Fig. I). One of the reasons of this effect can be the indenter tip change. The film changes the indenter geomet1y, indenter tip becomes more obtuse when film thickness increase and it's action becomes softer.