Three oligo[(1,2-propanediamine)-alt-(oxalic acid)] thin films were prepared on SiO2, R-plane sapphire, and MgO(100) substrates, and their proton conductivities were investigated. Conductivity depended on the substrate and varied from 4 x 10(-3) to 1 x 10(-4) S cm(-1) under the same conditions (80% relative humidity and 298 K). The thin films between the R-plane (1102) sapphire and MgO(100) substrates showed different molecular oriented structures. The thin film on the sapphire substrate, which shows higher proton conductivity, has a structure oriented parallel to the substrate. The molecular orientation in the thin film could be correlated with the proton-transport properties.