Ln(Sr,Ca)(3)(Fe,Co)(3)O-10 (Ln = La and Nd) + Gd0.2Ce0.8O1.9 (GDC) composites have been investigated as cathodes for intermediate temperature solid oxide fuel cells (IT-SOFC). The effects of GDC incorporation on the thermal and electrical properties, phase stability, and catalytic activity for the oxygen reduction reaction (ORR) of the Ln(Sr,Ca)(3)(Fe,Co)(3)O-10 intergrowth oxide have been studied. The Ln(Sr,Ca)(3)(Fe,Co)(3)O-10 + GDC (50:50 vol %) composite cathode exhibits lower thermal expansion coefficients (TEC) of similar to 16 x 10(-6)degrees C-1 in the range of 80-900 degrees C as well as lower polarization resistance compared to those of the pure Ln(Sr,Ca)(3)(Fe,Co)(3)O-10 cathodes. The NdSr2.5Ca0.5Fe1.5Co1.5O10 + GDC composite cathode shows the lowest polarization resistance (0.15 Omega cm(2) at 750 degrees C) and best electrochemical performance with maximum power densities of 615 mW cm(-2) at 800 degrees C (electrolyte-supported single cell with 500 mu m thick LSGM electrolyte), and 357 mW cm(-2) at 700 degrees C (anode-supported single cell with 20 mu m thick GDC electrolyte). The improved performance of NdSr2.5Ca0.5Fe1.5Co1.5O10 + GDC is attributed to the extended triple-phase boundary (TPB), enhanced oxide ion conductivity, and decreased TEC that provides good compatibility with those of standard SOFC electrolytes. (C) 2011 The Electrochemical Society. [DOI: 10.1149/1.3621718] All rights reserved.