A circuit substrate including a laminated layer, an embedded electronic device, at least a circuit structure, and a solder mask layer is provided. The embedded electronic device is disposed within the laminated layer. The circuit structure is disposed on a surface of the laminated layer and is connected between a reference plane and the embedded electronic device. In addition, the solder mask layer is disposed on the surface of the laminated layer and exposes a portion of the circuit structure. The circuit structure has a specific layout by which a circuit trace with an adjustable length can be formed by disconnecting or connecting the exposed portion of the circuit structure.