A rectangular alkaline storage battery includes an electrode plate which can be easily prepared and has a high packing density of active material and volumetric energy density. A connected negative electrode plate with hydrogen-absorbing alloy negative electrode plates is bent into a U-shaped form at a central portion (connecting portion). A composite positive electrode plate is then sandwiched by the hydrogen-absorbing alloy negative electrode plates with a separator made of an unwoven polypropylene fabric provided interposed therebetween to prepare an electrode plate unit. Two such electrode plate units are then laminated to form a group of electrode plates.