Mixed Pd-Sn colloidal systems are used to activate nonconductor surfaces for electroless metal deposition. The ways to prepare the colloidal solution (temperature, pH, reaction time) and the aging process have an effect on the size and the structure of the adsorbed Pd-Sn nuclei. The studies are supported by high resolution transmission electron microscopy observations, and selective area electron diffraction, energy-dispersive x-ray spectroscopy, and Rutherford backscattering spectroscopy analyses.