Yttria-stabilized zirconia (YSZ) films were synthesized by atomic layer deposition (ALD). Tetrakis(dimethylamido)zirconium and tris(methylcyclopentadienyl)yttrium were used as ALD precursors with distilled water as oxidant. From X-ray photoelectron spectroscopy (XPS) compositional analysis, the yttria content was identified to increase proportionally to the pulse ratio of Y/Zr. Accordingly, the target stoichiometry ZrO₂/Y₂O₃ = 0.92:0.08 was achieved. Crystal and grain structures of ALD YSZ films grown on amorphous Si₃N₄ were analyzed by X-ray diffraction (XRD) and atomic force microscopy (AFM). The microstructure of the polycrystalline films consisted of grains of tens of nanometers in diameter. To evaluate ALD YSZ films as oxide ion conductor, freestanding 60 nm films were prepared with porous platinum electrodes on both sides of the electrolyte. This structure served as a solid oxide fuel cell designed to operate at low temperatures. Maximum power densities of 28 mW/cm², 66 mW/cm², and 270 mW/cm² were observed at 265 °C, 300 °C, and 350 °C, respectively. The high performance of thin film ALD electrolyte fuel cells is related to low electrolyte resistance and fast electrode kinetics. The exchange current density at the electrode−electrolyte interface was approximately 4 orders of magnitude higher compared to reference Pt-YSZ values.