A package structure and method of forming the same are provided. The package structure includes a die, a via, an encapsulant, an adhesion promoter layer, and a polymer layer. The via is laterally aside the die. The encapsulant laterally encapsulates the die and the via. The adhesion promoter layer is sandwiched between the via and the encapsulant. The encapsulant comprises a portion aside the via and under the adhesion promoter layer, and the portion of the encapsulant is sandwiched between the adhesion promoter layer and the polymer layer.