$$\hbox {BaCeO}_3$$ BaCeO3 -based perovskites are well-known proton and oxygen ion conductors. For practical applications as electrolytes in solid oxide fuel cells, these compounds must be robust towards reduction of cerium ion. In this work, we explore the effect of reducing atmosphere on the physical properties of undoped and Nb-doped $$\hbox {BaCeO}_3$$ BaCeO3 . The $$\hbox {BaCeO}_3$$ BaCeO3 perovskite structure is thermodynamically stable at least up to 1450 $$^{\circ }\hbox {C}$$ ∘C upon annealing in $$\hbox {H}_2$$ H2 -containing atmosphere. Annealing at 1550 $$^{\circ }\hbox {C}$$ ∘C causes a decomposition of the $$\hbox {BaCeO}_3$$ BaCeO3 . The higher annealing temperature leads to higher concentration of $$\hbox {Ce}^{3+}$$ Ce3+ ions and a higher electrical conductivity. With increasing the annealing temperature from 1300 to 1450 $$^{\circ }\hbox {C}$$ ∘C , the activation energy of conductivity decreases from $$\hbox {E}_a$$ Ea = 0.31–0.263 eV. We attribute the electrical conductivity in reduced $$\hbox {BaCeO}_3$$ BaCeO3 to the activation of the small polaron hopping in agreement with the recent first-principles calculations. However, in contrast to the theoretical predictions, we find no evidence of the $$\hbox {Ce}^{3+}$$ Ce3+ –$$\hbox {Ce}^{3+}$$ Ce3+ spin-singlet small bipolarons.