Liquid crystal based sulfonic acid, 4-(octadecyloxy)phenylsulfonic acid, 1, effectively transports protons at 80 °C under non-humidified conditions. At its smectic A liquid crystal state, the proton conductivity of 1 was measured to be 1.1 × 10⁻² S cm⁻¹. The proton conductivities of 1 at its molten and solid powder states were found to be 1.2 × 10⁻⁴ and 1.5 × 10⁻⁷ S cm⁻¹, respectively. A lamellar structure of bilayer stacks of 1 with the sulfonic acid groups in a head-to-head configuration was found within the monodomain of SmA phase of 1 from in situ XRD and DFT calculation. We proposed that the efficient proton transporting property of 1 is highly correlated to the formation of supramolecular pathways between the molecules at its liquid crystal phase. Copyright © 2010 The Royal Society of Chemistry.