Rutherford backscattering (RBS) was used to determine the thickness and composition of several micrometers thick electroless-plated Pd/Ag alloy layers deposited on porous α-alumina. To determine the composition of the alloy, the thickness of the Pd layer after the first synthesis step and the thickness of the Pd/Ag sandwich structure after the second synthesis step were determined. The error in the determined thicknesses (± 5%) is much smaller than for the commonly used techniques, i.e., the weight difference and the scanning electron microscopy (SEM) cross-section method. RBS allows accurate determination of plating rates and an even more accurate value for the composition, since the error in the thickness is mainly systematic. This enables one to tune the synthesis parameters for layer thickness and alloy composition. A further and very important advantage of RBS is that pore filling of the support can be studied. Results showed that Pd penetrates into the alumina support during plating, with RBS it could be detected up to 1.4 μ m deep. It is estimated that the equivalent of 0.1 μ m bulk Pd is present in the pores of the support of typical electroless-plated samples. © 2005 Elsevier B.V. All rights reserved.