It is an object of the invention to provide a process for production of a thin-film capacitor that can simultaneously achieve improved capacity density and reduced leakage current density for barium strontium titanate thin-films. There is provided a process for production of thin-film capacitors that includes a metal oxide thin-film forming step in which an organic dielectric starting material is fired to form a barium strontium titanate thin-film, wherein the firing atmosphere used is an oxygen-containing inert gas atmosphere, and the barium strontium titanate thin-film formed by the process has a larger capacity density than the capacity density of the barium strontium titanate thin-film fired in an oxygen atmosphere.