Ultra-thin ZrO2-doped CeO2 (ZDC) interlayers (20 nm thick) with varying doping ratios of 0, 20, and 60 mol% were prepared using atomic layer deposition (ALD), and were investigated as cathodic interlayers for low-temperature solid oxide fuel cells (LT-SOFCs). The inclusion of ZrO2 in CeO2 film induced the reduction of Ce4+ to Ce3+ with higher concentration of oxygen vacancies, and also enhanced the resistance of the film to the coarsening at elevated temperature (800 degrees C), well preserving the nanoscale fine grain structure. As a result, the maximum power density of the cell with 20 mol%-doped ZDC interlayer improved by 57% compared to the cell without the interlayer due to enhanced activation process at the cathode, which seems to be due to higher oxygen vacancy population as well as higher grain boundary density at the electrolyte-cathode interface.