A method for manufacturing a wing box for aircraft, comprising the steps of: a1) arranging, on a curing surface, a first panel, in a composite material, comprising a skin having a first side and a plurality of stringers that extend parallel to a longitudinal direction (x); a2) providing a plurality of ribs, in non-polymerized composite material, each comprising a plate, a first pair of flanges and a second pair of flanges, each pair of flanges (15a, 15b) being arranged at opposite ends of said plate; a3) providing at least one tool, each tool having a first lateral surface and a second lateral surface, opposite to the first lateral surface, and comprising a central part, a bottom part and a top part, wherein the central part of each tool is interposed between said bottom part and said top part of each tool and may be pulled out in a transverse direction (y); b) alternately arranging a rib on said first side of the first panel along the transverse direction (y), by placing the first pair of flanges on said first side of the first panel, and a tool, between each pair of consecutive ribs and in contact with both of them; c) arranging a second panel, in a composite material, comprising a skin, having a first side, and a plurality of stringers that extend along a longitudinal direction (x), by putting said second panel in contact with the second pair of flanges of each rib; d) pulling out the central part of each tool along the transverse direction (y) and subsequently removing the top part and the bottom part of each tool; and e) having the first panel, the second panel, and each rib undergo a curing process in autoclave with vacuum bag, according to a specific pressure and temperature cycle, for curing the non-polymerized components. a1) arranging, on a curing surface, a first panel, in a composite material, comprising a skin having a first side and a plurality of stringers that extend parallel to a longitudinal direction (x); a2) providing a plurality of ribs, in non-polymerized composite material, each comprising a plate, a first pair of flanges and a second pair of flanges, each pair of flanges (15a, 15b) being arranged at opposite ends of said plate; a3) providing at least one tool, each tool having a first lateral surface and a second lateral surface, opposite to the first lateral surface, and comprising a central part, a bottom part and a top part, wherein the central part of each tool is interposed between said bottom part and said top part of each tool and may be pulled out in a transverse direction (y); b) alternately arranging a rib on said first side of the first panel along the transverse direction (y), by placing the first pair of flanges on said first side of the first panel, and a tool, between each pair of consecutive ribs and in contact with both of them; c) arranging a second panel, in a composite material, comprising a skin, having a first side, and a plurality of stringers that extend along a longitudinal direction (x), by putting said second panel in contact with the second pair of flanges of each rib; d) pulling out the central part of each tool along the transverse direction (y) and subsequently removing the top part and the bottom part of each tool; and e) having the first panel, the second panel, and each rib undergo a curing process in autoclave with vacuum bag, according to a specific pressure and temperature cycle, for curing the non-polymerized components.