A package substrate and a method for forming the package substrate are disclosed. The package substrate includes an interposer having a plurality of conductive through vias and a first insulating layer formed on the sidewalls of the conductive through vias, a second insulating layer formed on one side of the interposer, and a plurality of conductive vias formed in the second insulating layer and electrically connected to the conductive through vias. By increasing the thickness of the first insulating layer, the face diameter of the conductive through vias can be reduced, and the layout density of the conductive through vias in the interposer can thus be increased.