The conditions necessary for synthesizing thin oxide superconductor films in vacuum deposition systems are described. It is shown that the oxygen partial pressure on the substrate kept at the crystallization temperature must be higher than the oxygen dissociation pressure of the multicomponent oxide films. This condition can be satisfied for the YBa₂Cu₃O_7-δ-O₂ system when the oxygen partial pressure lies in the range 10^-110^-2mb at the substrate temperatures of 800-900K. For the Bi-Sr-Ca-Cu oxide system, the number of CuO layer in a unit cell can be controlled by utilizing the multilayer deposition technique. The multilayer films thus obtained have smooth surface and contain no grain boundaries or precipitates. The large solid-solubility found in these multilayered films shows the possibility of obtaining films consisting of non-equilibrium phase.