A separator for a valve regulated lead-acid battery comprises a paper sheet made by a wet papermaking process, mainly made of glass microfibers, wherein the separator is a structure having a three-layer laminated structure which comprises two thin-fiber layers and one thick-fiber layer, wherein the two thin-fiber layers cover both surfaces of the thick-fiber layer in the thicknesswise direction of the separator to constitute the three-layer laminated structure, wherein each of the thin-fiber layers is made of glass fibers having an average fiber diameter of 0.4 to 1.0 μm as the glass microfibers and has an average pore diameter of 3.5 μm or less, and the thick-fiber layer is made of glass fibers having an average fiber diameter of 1.3 to 4.0 μm as the glass microfibers and has an average pore diameter which is 4.0 μm or more and which is 1.5 times or more that of the thin-fiber layer, wherein the average fiber diameter of the glass fibers in the all layers of the separator is 1.2 μm or more, and the thickness ratio of the thin-fiber layers to the thick-fiber layer in the all layers of the separator is 10/90 to 50/50. In the valve regulated lead-acid battery, both the improvement of the compressive force lowering prevention and the improvement of the electrolyte stratification prevention can be achieved, improving the movement property of the electrolyte within the separator.