A package structure including a first die, an encapsulant, a first circuit structure, a second circuit structure, a conductive connector, a second die, and a filler is provided. The encapsulant covers the first die and has a first surface and a second surface opposite to each other. The first circuit structure is disposed on the first surface. The second circuit structure is disposed on the second surface. The conductive connector penetrates the encapsulant. The second die is disposed on the second circuit structure. The second die has an optical signal transmission area. The filler is disposed between the second die and the second circuit structure. An upper surface of the second circuit structure has a groove. The upper surface includes a first area and a second area disposed on opposite sides of the groove. The filler directly contacts the first area. The filler is disposed away from the second area.