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) approximate to 1-5 mu m) are used to compare the effect of the crystal structure: the cubic La0.5Ba0.5CoO3-delta with La/Ba cations randomly distributed, and a tetragonal LaBaCo2O6-delta with La/Ba layered distribution. In addition, the effect of microstructure is studied by using a newsol-gel route which allows obtaining LaBaCo2O6-delta with smallest particle size (d(p) approximate to 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,R-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. (C) 2016 Elsevier Ltd. All rights reserved.