There is disclosed a multilayer insulated wire which comprises a conductor and solderable extrusion-insulating layers made up of two or more layers for covering the conductor, wherein at least one insulating layer is formed by a mixture comprising 100 parts by weight of a resin (A), of at least one selected from the group consisting of polyetherimide resins and polyethersulfone resins, 10 parts by weight or more of a resin (B), of at least one selected from the group consisting of polycarbonate resins, polyarylate resins, polyester resins, and polyamide resin, and 15 to 200 parts by weight of an inorganic filler (C). There is also disclosed a transformer which utilizes the multilayer insulted wire. The multilayer insulated wire is excellent in heat resistance, solderability, high-frequency characteristic, and coilability, and it is favorably suitable for industrial production. Further, the transformer utilizing the multilayer insulated wire is excellent in electrical properties and high in reliability, since when used at high frequencies, electric properties are not lowered and influence by the generation of heat can be prevented.