This paper reports on the mechanical behaviour of nanostructured W/Cu thin films deposited on Kapton (R) under controlled biaxial loadings thanks to a biaxial testing device developed on DiffAbs beamline at SOLEIL synchrotron (Saint-Aubin, France). In situ tensile tests were carried out combining 2D synchrotron X-ray diffraction (XRD) and digital-image correlation (DIC) techniques. First, the elastic behaviour of the composite metallic film - polymeric substrate was investigated under equi-biaxial and non-equi-biaxial loading conditions. The results show that the strain measurements (in the crystalline film by XRD and the substrate by DIC) match within 10(-4). This result demonstrates the full transmission of strains in the elastic domain through the film-substrate interface and thus a good adhesion of the thin film to the substrate. The second part of the paper deals with higher strains response under equi-biaxial tensile tests. The elastic limit of the nanostructured W/Cu thin films was determined at the bifurcation point between strains obtained by XRD and DIC. Deformation mechanisms such as strain localisation and film fragmentation are proposed. (C) 2012 Elsevier B. V. All rights reserved.