The reaction mechanism for electrochemical‐vapor deposition of yttria‐stabilized zirconia was studied. Yttria‐stabilized zirconia films were deposited on porous La(Sr)MnOxusing the electrochemical‐vapor‐deposition process. The distribution of yttria concentration through the film was investigated by means of secondary‐ion‐mass spectroscopy and x‐ray microanalysis and found to be nearly constant. The deposition rate was approximately proportional to the minus two‐thirds power of the film thickness, the one‐third power of the partial pressure of ZrCl4/YCl3mixed gas, and the two‐thirds power of the product of the reaction temperature and the electronic conductivity of yttria‐stabilized zirconia film. These experimental results were explained by a model for electron transport through the YSZ film and reaction between the surface oxygen and the metal chloride on the chloride side of the film, both of which affect the deposition rate. If the film thickness is very small, the deposition rate is thought to be controlled by the surface reaction step. On the other hand, if large, the electron transport step is rate controlling.