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This work discusses the effect of the crystal structure and microstructure on the electrocatalytic activity of Lanthanum-Barium cobaltite (LBC), evaluatedas IT-SOFC cathode. Two systems with similar microstructures (particle sizes d p ≈ 1–5 μm) are used to compare the effect of the crystal structure: the cubic La 0.5 Ba 0.5 CoO 3-δ with La/Ba cations randomly distributed, and a tetragonal LaBaCo 2 O 6-δ with La/Ba layered distribution. In addition, the effect of microstructure is studied by using a newsol-gel route which allows obtaining LaBaCo 2 O 6-δ with smallest particle size (d p ≈ 500 nm). The electrode reaction isstudied by electrochemical impedance spectroscopy (EIS) as a function of temperature (T) and oxygen partial pressure (pO 2 ). The electrode polarization resistance (R C,P ) presents two contributions, a low frequency (R LF ) and a high frequency Gerischer-resistance (R G ). On one side, R LF , associated to the O 2 -gas diffusion across the gas layer boundary, presents low activation energy (E a ) and is proportional to pO 2 −1 , presenting the same values regardless the microstructure.On the other side, R G is in agreement with anO 2 -reduction mechanismco-limited by O-surface exchange and O-bulk diffusion. R G is strongly influenced by structure (trough the diffusion coefficient D V ) and microstructure (inversely proportional to d p ). Besides, R G decreases by reducing d p and by modifying the La/Ba ordering from layered to randomly distributed. [ABSTRACT FROM AUTHOR]