<p>The study examined the effect of polyvinyl alcohol (PVA) crosslinked with sulfosuccinic acid on the structure, morphology, physico-mechanical and electrochemical properties of composite membranes made of the domestic perfluorinated copolymer (an analog of Nafion) and PVA. An increase in the content of crosslinked PVA in the membrane leads to an increase in the proton conductivity. The degree of crystallinity of the composites depends on the content of the crosslinking agent. The morphology of the membrane surfaces is significantly different. Thus, the lower surface has a uniform microstructure, whereas the upper surface forms three-dimensional folded structures by the self-organization of the polymer chains in the surface layer. According to the energy-dispersive analysis, the two layers of the membrane significantly differ in the chemical composition, as illustrated by the distribution profile of fluorine over the membrane thickness. The observed structural and morphological features of the membranes account for the differences in their proton conductivity.</p>