PURPOSE: To provide a battery separator made of a nonwoven fabric with high short circuit preventing performance, high electrolyte holding capability for an electrode in charge/discharge cycles, high gas permeation capability, and sufficient mechanical strength.

CONSTITUTION: A battery separator is made of a nonwoven fabric comprising thermoplastic fibers and heat-fusible fibers which are heat-fused to bond fibers, and having raising on the surface on at least one side of the nonwoven fabric. The thermoplastic fibers and the heat-fusible fibers are three-dimensionally entangled by water stream, and the heat-fusible fibers are heat-fused to bond fibers to obtain a wet type nonwoven fabric. A raising treatment is conducted on the surface of at least one side o the nonwoven fabric prepared by an entangling treatment in which water steam is struck to a fiber web comprising the thermoplastic fibers and the heat-fusible fibers, or by a heat treatment in which the heat-fusible fibers are melted to bond fibers without conducting the entangling treatment. A sealed secondary battery in which the battery separator is arranged is obtained.