A nonaqueous secondary battery separator, disposed between a cathode and an anode, includes: a porous base material containing a polyolefin as a main component; and a porous layer containing a polyvinylidene fluoride-based resin on at least one surface of the porous base material. The separator satisfies (C)/(D)≤0.13, where (C) represents the average pore diameter (μm) of the porous base material, and (D) represents the porosity of the porous base material, in the porous layer after being immersed for 24 hours in an electrolyte solution having a temperature of 25° C. in which electrolyte solution LiPF6 having a concentration of 1.0 mole per liter is dissolved in a mixed solvent containing ethyl methyl carbonate, diethyl carbonate, and ethylene carbonate at a volume ratio of 50:20:30, the resin having absorbed the electrolyte solution having a volume of 0.05 to 5.00 cm3 per square meter of the porous layer.