The present process for removing residual water molecules is suitably used in a metallic thin film production method of forming a metallic thin film on a substrate. The residual-water-molecule removal process involves removing residual water molecules using a gas generated by vaporizing a purge solvent. Preferably, the purge solvent is an organic solvent or an organic solvent composition having a water content at the azeotropic composition of at least 20% by mass. With the present residual-water-molecule removal process, water molecules remaining in the system can be removed efficiently in the production of metallic thin films by the ALD method or the like, and thus, the film-formation time can be shortened and metallic thin films can be produced efficiently.