Abstract: The paper is devoted to the study of the conduction mechanism in perovskite phases with composition La2 Me +3ZnO5.5 (Me +3 = Al3+, Sc3+, In3+). The phases were synthesized by a standard ceramic technique in the 700–1300°C temperature range. The structure of the La2InZnO5.5 and La2ScZnO5.5 samples is orthorhombic, while the La2AlZnO5.5 sample crystallizes in the cubic symmetry. The electrical conductivity of La2Me+3ZnO5.5 (Me+3 = Al3+, Sc3+, In3+) samples is studied as a function of temperature (200–900°C), oxygen partial pressure pO2, and humidity pH2O. The complex oxides are found to have a mixed type of conduction in air, the electronic contribution (the p-type conduction) increases with increasing temperature. The phases exhibit the dominant oxygen-ion transport at temperatures below 500°C. In wet atmosphere, Sc3+- and In3+-containing samples are capable of incorporating water from gas phase and forming proton defects. No significant proton transport in the La2AlZnO5.5 sample is realized. The partial conductivities (Formula presented.) , σh in a wide range of temperatures and рО2 are discussed. © 2023, Pleiades Publishing, Ltd.