© 2020 The Physical Society of Japan. Proton conducting materials that can work without humidification and above 100 °C have been highly desired for future fuel cells, and thus development of high-performance anhydrous proton conductors and elucidation of proton conduction mechanism are pivotal issues. Those based on organic crystals allow us to investigate the proton conduction mechanism in detail by utilizing rich material designability of organic molecules. In this study, we investigated structure–property relationship and effect of molecular dynamics of constituent molecules on the proton conductivity using high-quality single crystals of a series of imidazolium hydrogen dicarboxylates. As a result, “intrinsic” proton conductivities of these salts without contributions from grain boundaries were observed for the first time. Interestingly, our investigation revealed that not only the “static” H-bond network structures but also the “dynamics” of the constituent molecules synergistically play important roles in the anhydrous proton conduction of these salts, which is thought as peculiar nature of Grotthuss-type conduction in anhydrous solids. The results provide crucial insights into conduction mechanism and novel material design of the anhydrous proton conductors.