Composite materials based on MF-4SK perfluorosulfonic acid membranes and silver nanoparticles with various distribution of the metal in the membrane matrix have been prepared. The influence of the concentration of a reducing agent on the distribution of silver particles in the bulk of the membrane has been revealed. It was shown that under certain conditions a conductive layer of reduced silver is formed on the membrane surface. The dependence of the diffusion permeability of the obtained mixed-matrix membranes on the quantity of the introduced silver and its spatial distribution within the membrane matrix has been determined.