Cu UPD on Pt(111) has been studied by XANES and EXAFS in the fluorescence mode, under grazing and normal X-rays SO2-incidence, in two electrolytic mediums (sulfate solution and chlorine one). For a complete deposited Cu monolayer, with 4 anions, oxygen atoms in atop site with respect to copper atoms are detected clearly. The Cu-Cu interatomic distance deduced from EXAFS calculations is smaller than the Pt-Pt distance, 2.68 Angstrom instead of 2.77 Angstrom, while quantitative XANES data analysis is coherent with an epitaxial growth of Cu on Pt(111). We conclude that Cu full layer is composed of bidimensional domains, with (1 x 1) and threefold hollow sites. In presence of chloride anions, oxygen atoms are replaced by chlorine ones, providing a (V 3 x root3)R30degrees superstructure, while copper atoms adopt the same (I x 1) and threefold hollow sites configuration.