A nonaqueous electrolyte secondary battery separator which has a low shutdown temperature, a high mechanical strength, and a high ion permeability is provided. The nonaqueous electrolyte secondary battery separator contains a polyolefin-based resin as a main component. The nonaqueous electrolyte secondary battery separator has a maximum heating value of not less than 30 mW/g observed during isothermal crystallization of the nonaqueous electrolyte secondary battery separator at 128° C.