A manufacturing method of a circuit substrate includes the following steps. The peripheries of two metal layers are bonded to form a sealed area. At least a through hole passing through the sealed area is formed. Two insulating layers are formed on the two metal layers. Two conductive layers are formed on the two insulating layers. The two insulating layers and the two conductive layers are laminated to the two metal layers bonded to each other, wherein the metal layers are embedded between the two insulating layers, and the two insulating layers fill into the through hole. The sealed area of the two metal layers is separated to form two separated circuit substrates. Therefore, the thinner substrate can be operated in the following steps, such as patterning process or plating process. In addition, the method may be extended to manufacture the circuit substrate with odd-numbered layer or even-numbered layer.