Numerous sulfonated polymer electrolyte membranes (PEMs) have been developed for direct methanol fuel cells (DMFCs) during the last decade. An analysis for DMFC PEMs obtained from the literature data and structural information is presented based on non-traditional length scale parameters. The analysis presented highlights specific differences in chemical composition between PEMs including perfluorinated sulfonic acids, hydrocarbon-based and polymers having specific interactions. Differences in cross-linked, homopolymer-like, random and multi-block polymer architectures are also discussed. The analysis presented gives important insight into molecular design aspects of sulfonated PEMs for DMFCs.Highlights► Structural effects of polymer electrolyte membranes for direct methanol fuel cells are investigated using length scale parameters. ► Desirable properties are obtained with high sulfonic acid concentration and low water uptake. ► Strategic approach to improve the membrane properties is demonstrated.