A multilayer flexible wired circuit board that can provide high density wiring and also can provide reduction in thickness and size, and a producing method thereof. A four-layered flexible wired circuit board is produced by preparing a double-sided substrate in which a first conductor layer and a second conductor layer are laminated on both sides of a first insulating layer; preparing a first single-sided substrate in which a third conductor layer is laminated on one surface of a second insulating layer and a second single-sided substrate in which a fourth conductor layer is laminated on one surface of a third insulating layer; bonding the first conductor layer and the third conductor layer to each other through a first thermosetting adhesive layer; and bonding the second conductor layer and the fourth conductor layer to each other through a second thermosetting adhesive layer.