Optical elements are provided. An optical element is formed by injecting resin material into a mold through a gate in a first direction. The optical element includes a main body, a flange surrounding and connecting the main body, and a curved depression formed between the main body and the flange. The main body has a central axis and a first curved surface. The flange includes an annular abutting surface and a connecting portion. The connecting portion has a connecting surface connecting the first curved surface and the abutting surface. Both of the abutting surface and the connecting surface are perpendicular to the central axis.