W x Zr 1−x thin films were deposited at room temperature on glass substrates by co-sputtering tungsten and zirconium targets in argon. The composition was found in the range 0≤x≤0.81. The grain size deduced from X-ray diffraction analysis ranged from 1.3nm to 16nm depending on the composition. The events in the resistivity, optical reflectivity and thickness evolutions were correlated with the X-ray diffraction analysis. Depending on the composition, the local organization can be attributed to a nanocrystalline solid solution of W in Zr, to a nanocomposite structure involving ZrW 2 nanograins embedded in an amorphous matrix, to ZrW 2 Laves phase nanograins and to a nanocrystalline solid solution of Zr in W. For 0<x≤0.72, the equivalent grain size is very small (less than 2nm) and the evolution of the resistivity can be fitted by the estimated volume of the material perturbed by the grain boundaries.