The problem addressed by the invention lies in providing a method for producing an inorganic substance powder highly-oriented thin film sheet with which it is possible to produce a sheet of uniform thickness while preventing the generation of impurities, improving sheet surface properties, adjusting apparent specific gravity, and the like. The method for producing a thin film sheet comprises a step for preparing a predetermined inorganic substance powder, thermoplastic resin, and auxiliary agent, a step for exposing the starting materials mixed at a predetermined mixture ratio to high shear stress while kneading, a step for feeding the kneaded starting materials to a T die-type extrusion molding device and molding a sheet, and a step for adjusting the apparent gravity as desired by stretching under predetermined conditions.