A fabrication method of a packaging substrate includes: providing a metal board having a first surface and a second surface opposite to the first surface, wherein the first surface has a plurality of first openings for defining a first core circuit layer therebetween, the second surface has a plurality of second openings for defining a second core circuit layer therebetween, each of the first and second openings has a wide outer portion and a narrow inner portion, and the inner portion of each of the second openings is in communication with the inner portion of a corresponding one of the first openings; forming a first encapsulant in the first openings; forming a second encapsulant in the second openings; and forming a surface circuit layer on the first encapsulant and the first core circuit layer.