Investigation of the electrical conductivity behavior of layered perovskite oxides, H2Ln2Ti3O10 (Ln = La, Nd, Sm and Gd), has revealed that the materials exhibit moderate conductivity (approximately 10(-5) OMEGA-1 cm-1 at 400-degrees-C) in hydrogen atmosphere, that is likely to be protonic in origin. It is suggested that the anion-deficient layered perovskite, Ln2Ti3O9 square, formed in situ by dehydration, may interact with water vapor in hydrogen atmosphere in a manner analogous to that of yttria-doped BaCeO3 and SrCeO3 giving rise to the protonic conductivity. HLa2Ti2NbO10 and HCa2Nb3O10 possessing a slightly different layered perovskite structure, exhibit a higher conductivity (approximately 10(-4)-10(-3) OMEGA-1 cm-1) under the same conditions.