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

Provided is a separator for a non-aqueous secondary battery, the separator contains a porous substrate, and a heat resistant porous layer that is provided on one side or on both sides of the porous substrate, and that contains a heat resistant resin and barium sulfate particles, in which an average primary particle size of the barium sulfate particles contained in the heat resistant porous layer is from 0.01 μm to less than 0.30 μm, and in which a volume ratio of the barium sulfate particles in a solid content portion of the heat resistant porous layer is from 5% by volume to less than 30% by volume.