This study uses X-ray diffraction (XRD) techniques to investigate the nanostructural features of a series of four Pd/C catalysts, which had the same load, 0.51 +/- 0.02 wt%, as palladium, with significantly different dispersions, obtained by applying different temperature ageings up to 873 K. By means of a Rietveld refinement, performed using a special fitting procedure, which takes into account the various contributions to the background scattering, the palladium fraction due to nanoparticles or clusters smaller than about 20-25 Angstrom could be determined. We have compared this Rietveld (absolute) quantitative method with a simpler, but less precise, single-peak (relative) XRD analysis, interesting for fast industrial applications. The Pd fractions due to nanoparticles, as determined by the two methods, are close each other for all samples investigated, apart from one for which the disagreement is near 20%.