A package structure and method of forming the same are provided. The package structure includes a die, a TIV, an encapsulant, a RDL structure, an underfill layer, a protection layer, and a cap. The TIV is aside the die. The encapsulant laterally encapsulates the die and the TIV. The RDL structure is electrically connected to the die. The underfill layer is disposed between the die and the RDL structure and laterally encapsulated by the encapsulant. The protection layer is overlying the die and the encapsulant. The cap covers a top surface of the TIV and laterally aside the protection layer. A top surface of the cap is higher than a top surface of the encapsulant and lower than a top surface of the protection layer.