A separator which includes a covering layer in which a fine framework of polyolefin resin is coated with a glass layer and an exposed layer in which the polyolefin resin is exposed is provided. A battery is provided having a cathode and an anode, an electrolyte, and a separator where the separator has the covering layer in which the fine framework of polyolefin resin is coated with the glass layer and a method for manufacturing a separator including the step of coating a fine framework of polyolefin resin with the glass layer by applying a precursor containing viscous liquid product which contains only polysilazane compound or a mixture of viscous liquid product which contains only polysilazane compound with polycarbosilazane compound to the polyolefin resin and placing the precursor applied polyoleline resin in a water bath to dry.