A separator for a valve regulated lead-acid battery which comprises a paper sheet where very fine glass fiber is a main component, which has a piercing strength (puncture strength) of 4.5 N/mm or more and a tensile strength of 7.0 N/10 mm2 or more. The paper sheet is made by blending 80 to 90% by weight of glass fiber having 1.5 μm or less average fiber size, 5 to 10% by weight of single-material monofilament-form thermally non-adhesive organic fiber (non-heat-bondable organic fiber) and 5 to 10% by weight of single-material monofilament-form thermally adhesive organic fiber (heat-bondable organic fiber) comprising the same kind of material as in the thermally non-adhesive organic fiber in a wet papermaking process whereupon the fiber materials are bonded each other by thermal fusion of the thermally adhesive organic fiber whereby a coat (film) by melting of the organic fiber is not substantially formed on the surface of the glass fiber.