Separator for non-aqueous secondary battery and non-aqueous secondary battery

Provided is a separator for a non-aqueous secondary battery containing a porous substrate; and a porous layer that is provided on one side of the porous substrate, and that contains a resin and a filler, in which a shrinkage ratio in a MD direction, when heat-treated at 100° C. for 30 minutes under no tension, is more than 1.2% and less than or equal to 3.5%.