In the present study, the polarization characteristics of La0.6Sr0.4CoO3 - delta (LSC)-Gd0.1Ce0.9O2 - delta (GDC) composite cathodes for solid oxide fuel cell (SOFC) with different volume ratios were experimentally evaluated. The target volume ratios of LSC:GDC = 20:80, 30:70, 50:50, 70:30, 100:0% cathodes were fabricated by screen printing method. Current-voltage curve and electrochemical impedance spectroscopy (EIS) measurements were conducted at 700 degrees C under 100% oxygen. The best performance was achieved at a volume ratio of LSC:GDC = 30:70%. Three dimensional microstructures of composite cathodes were reconstructed by focused ion beam scanning electron microscope (FIB-SEM). Microstructural parameters were quantified and correlated with the polarization characteristics. Neither LSC surface nor three phase boundary (TPB) reactions can individually explain the total performance of the composite cathode. Effective ionic conductivity is monotonously enhanced as the volume ratio of GDC is increased due to its high ionic conductivity. Compared to La0.6Sr0.4Co0.2Fe0.8O3 - delta (LSCF)-GDC composite cathodes, overpotentials of LSC-GDC composite cathodes are lower regardless of the volume ratio. Pure LSC cathode shows small surface area due to high sinterability of LSC. Compared to LSCF-GDC composite, LSC:GDC = 50:50 and 70:30 vol% samples showed higher active TPB density due to the larger LSC-GDC interface area.