A manufacturing method of a circuit substrate includes the following steps. A core layer having a core dielectric layer, a first patterned circuit layer and a second patterned circuit layer is provided. An electroless plating nickel layer is formed on the first patterned circuit layer and the second patterned circuit layer. The electroless plating nickel layer has a first thickness, and the first thickness is between 1 micrometer and 10 micrometers. A reducing process is performed on the electroless plating nickel layer so that the electroless plating nickel layer is thinned from the first thickness to a second thickness to form a thinned electroless plating nickel layer. The second thickness is between 0.01 micrometers and 0.9 micrometers. An electroless plating palladium layer is formed on the thinned electroless plating nickel layer. A surface metal passivation layer is formed on the electroless plating palladium layer.