An object of the present disclosure is to provide a nonaqueous electrolyte secondary battery separator which has high heat resistance and is resistant to the detachment of a heat resistant layer. A nonaqueous electrolyte secondary battery according to an example embodiment includes a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode. The separator includes a polyolefin substrate and a heat resistant layer disposed on a side of the substrate. The heat resistant layer includes an aramid resin, and the aramid resin has a ratio (B/A) of 0.94 to 1.14 wherein A is the absorbance at a wavelength of 1318 cm−1 and B is the absorbance at a wavelength of 1650 cm−1 in an infrared absorption spectrum obtained by infrared spectroscopic measurement.