The structure of dry and hydrated perovskite La0.9Sr0.1ScO3 - delta has been studied by means of X-ray and neutron powder diffraction methods. Preferable positions for oxygen vacancies and deuterons in the oxide have been determined. Thermodynamics of water vapour uptake and transport phenomena have been experimentally investigated at pH(2)O = 0.24 atm and pO(2) = 0.18 atm in the temperature range from 300 to 950 degrees C. The enthalpy and entropy of hydration reaction have been calculated. The oxidation enthalpy for two possible mechanisms of hole transfer (band conduction and small polaron hopping) have been estimated. The electrical conductivity has been investigated by means of impedance spectroscopy measurements in the temperature range from 500 to 900 degrees C and at the oxygen partial pressures of 10(-20) atm < pO(2) < 0.21 atm. The oxygen surface exchange and diffusion coefficients have been obtained by means of the isotope exchange method with gas phase equilibration in the temperature range of 600-900 degrees C and at the oxygen partial pressure 0.01 atm. The dependences of the transference numbers of protons, oxygen ions and holes on external conditions have been determined. The La0.9Sr0.1ScO3 - delta oxide was found to be a pure protonic conductor at temperatures below 600 degrees C under reducing conditions.