An object of the invention is to provide a separator for a nonaqueous secondary battery, which has good adhesion to electrodes and is also capable of ensuring sufficient ion permeability even after attachment to electrodes. The separator for a nonaqueous secondary battery of the invention includes a porous substrate and an adhesive porous layer that is formed on at least one side of the porous substrate and contains a polyvinylidene-fluoride-based resin. The separator for a nonaqueous secondary battery is characterized in that the adhesive porous layer has a crystal size of 1 to 13 nm.