The preparation and characterization of nanoscale silver sulfide and silver particles in Nafion and perfluorinated sulfonimide ionomer membranes are reported. The results show that the nanoparticles are hosted in the membrane structure in an isolated fashion, with no indication of channels-like domains as proposed in the ion cluster model for the ionomer membranes. These randomly dispersed nanoparticles are also significantly larger than the average size of the reverse micelle-like hydrophilic cavities estimated in the literature for Nafion membrane. The properties of the silver sulfide and silver nanoparticles are presented, and their implications to the understanding of membrane nanoscopic structural details are discussed.