Provided is a package structure including a photonic die, an electronic die, a conductive layer, a circuit substrate, and an underfill. The electronic die is bonded on a front side of the photonic die. The conductive layer is disposed on a back side of the photonic die. The conductive layer includes a plurality of conductive pads and a dam structure between the conductive pads and a first sidewall of the photonic die. The circuit substrate is bonded on the back side of the photonic die through a plurality of connectors and the conductive pads. The underfill laterally encapsulates the connectors, the conductive pads, and the dam structure. The underfill at the first sidewall of the photonic die has a first height, the underfill at a second sidewall of the photonic die has a second height, and the first height is lower than the second height.