For producing an inter-layer conductive structure of a circuit board, an insulating layer, a first conductive layer, a second conductive layer and an electric contact material are provided, wherein the insulating layer includes at least a conductive hole therein. The electric contact material is inserted into the conductive hole of the insulating layer to form a conductive plug, and the first and second conductive layers are laminated to opposite surfaces of the insulating layer, respectively. After lamination, the conductive plug has two ends thereof in electric contact with the first conductive layer and the second conductive layer, respectively.