The present invention is to provide a separator that is excellent in heat resistance, shutdown function, flame retardancy and handling property. The separator for a nonaqueous secondary battery of the invention is a separator for a nonaqueous secondary battery that has a polyolefin microporous membrane at least one surface of which is laminated with a heat resistant porous layer containing a heat resistant resin, and is characterized by containing an inorganic filler containing a metallic hydroxide that undergoes dehydration reaction at a temperature of 200 to 400° C.