Disclosed are a separator for secondary batteries with enhanced stability and a method of manufacturing the separator. The separator can prevent self-discharge which may occur when a porous non-woven fabric material is used for a separator; can perform a shutdown function at a high temperature of 200° C. or less; and can avoid even under harsh conditions of high temperatures, deterioration in stability caused by internal short-circuit of positive and negative electrodes. In particular, the separator for secondary batteries of the present invention includes a porous non-woven fabric material impregnated with a baroplastic polymer powder and pores of the porous non-woven fabric material are filled with the baroplastic polymer powder by pressing an assembly of the secondary battery.