The piezoelectric coefficient for semiconductor nanowires (NWs) was suggested to show a non-linear increase with decreasing NW diameter making them promising candidates for future mechanical energy transducers. However, very few experimental works on the piezoelectricity of NWs exist due to the tiny extensions induced in nanostructures by piezoelectricity which are difficult to be quantified by techniques like piezo force microscopy. On the contrary, X-ray diffraction (XRD) is highly sensible to lattice deformations, thus facilitating to measure the piezoelectrically-induced strain and, hence provide absolute values of the piezoelectric coefficients of nanomaterials. This proposal focuses on the piezoelectric properties of single suspended ZnO NWs studied by in situ XRD while applying external electric fields.