The effect of donor doping Nb5+ → In3+ on the transport characteristics of the complex oxide BaLaInO4 with the Ruddlesden–Popper structure is analyzed. It is shown that the resulting phases are capable of dissociative absorption of water from the gas phase and manifestation of protonic conduction. It is found that the donor doping of BaLaInO4 leads to the increase in the oxygen-ionic conductivity.