Preparation of high-quality yttria-stabilized zirconia (YSZ) electrolyte films on porous substrates is critical to the fabrication of high-performance solid-state ionic devices such as fuel cells and gas sensors. An electrophoretic deposition (EPD) process is investigated for the preparation of YSZ electrolyte films on both porous La_0.85Sr_0.15MnO₃ (LSM) and porous LSM–YSZ composite substrates. The Pechini process is used for the preparation of fine LSM powders with an average particle size of about 0.1 μm. The processing parameters critically influencing the microstructures of green YSZ films are identified and optimized to obtain uniform, crack-free green YSZ films with high packing density of fine YSZ particles. Dense YSZ films with a thickness of about 10 μm have been successfully fabricated on both porous LSM and porous LSM–YSZ substrates when sintered at 1250°C for 2 h.