An embodiment of the present invention provides, as a nonaqueous electrolyte secondary battery separator excellent in cycle characteristic, a nonaqueous electrolyte secondary battery separator including a polyolefin porous film, wherein a ratio of a displacement amount of the nonaqueous electrolyte secondary battery separator at a 10th loading-unloading cycle to a displacement amount of the nonaqueous electrolyte secondary battery separator at a 50th loading-unloading cycle is in a range of 100% to 130%.