A method for forming a package structure is provided. The method includes forming first conductive structures and a first semiconductor die on a same side of a redistribution structure. The method includes forming an interposer substrate over the redistribution structure, wherein the first semiconductor die is between the interposer substrate and the redistribution structure, and edges of the interposer substrate extend beyond edges of the first semiconductor die. The method includes forming a second semiconductor die on the redistribution structure, wherein the first semiconductor die and the second semiconductor die are disposed on opposite sides of the redistribution structure.