Development of high performance cathodes with low polarization resistance is critical to the success of solid oxide fuel cell (SOFC) development and commercialization. In this paper, (La0.8Sr0.2)0.9MnO3 (LSM)–Gd0.2Ce0.8O1.9(GDC) composite powder (LSM ~70 wt%, GDC ~30 wt%) was prepared through modification of LSM powder by Gd0.2Ce0.8(NO3)x solution impregnation, followed by calcination. The electrode polarization resistance of the LSM–GDC cathode prepared from the composite powder was ~0.60 Ω cm2 at 750 °C, which is ~13 times lower than that of pure LSM cathode (~8.19 Ω cm2 at 750 °C) on YSZ electrolyte substrates. The electrode polarization resistance of the LSM–GDC composite cathode at 700 °C under 500 mA/cm2 was ~0.42 Ω cm2, which is close to that of pure LSM cathode at 850 °C. Gd0.2Ce0.8(NO3)x solution impregnation modification not only inhibits the growth of LSM grains during sintering but also increases the triple-phase-boundary (TPB) area through introducing ionic conducting phase (Gd,Ce)O2-δ, leading to the significant reduction of electrode polarization resistance of LSM cathode.