A polymer sheet according to at least one embodiment of the present invention is a polymer sheet whose main component is oriented nanocrystals of a polymer, and which satisfies the following conditions (I), (II), and (III): (I) having a crystallinity of not less than 70%; (II) having a tensile strength at break of not less than 100 MPa and a tensile modulus of not less than 3 GPa; and (III) having an average thickness of not less than 0.15 mm. According to at least one embodiment of the present invention, it is possible to provide a polymer sheet excelling in properties such as mechanical strength, heat tolerance, and transparency, particularly a polymer sheet having excellent properties such as mechanical strength, heat tolerance, and transparency in general-purpose plastics such as polypropylene.