A wired circuit board and a producing method thereof are provided which can precisely form an insulating layer and reduce transmission loss with a simple layer structure and also features excellent long-term reliability by preventing the occurrence of an ion migration phenomenon between a ground layer and a positioning mark layer, and the insulating layer to improve the adhesion therebetween and the conductivity of a conductor. A metal supporting board is prepared and a first metal thin film is formed on the metal supporting board. A resist is formed in a pattern and a ground layer and a positioning mark layer are formed on the first metal thin film exposed from the resist at the same time. A second metal thin film is formed over the ground layer and the positioning mark layer, then the resist is removed. An insulating base layer is formed on the first metal thin film including the upper surface of the second metal thin film, thereafter, a conductive pattern is formed on the insulating base layer.