Aircraft stringers having carbon fiber reinforced plastic (CFRP) material reinforced flanges are disclosed. An example stringer to be coupled to a skin of an aircraft comprises a flange. The flange includes a first portion of a first stiffening segment. The flange further includes a first portion of a second stiffening segment coupled to the first portion of the first stiffening segment. The flange further includes a CFRP reinforcement segment coupled to the first portion of the first stiffening segment and to the first portion of the second stiffening segment. The CFRP reinforcement segment strengthens the first portion of the first stiffening segment and the first portion of the second stiffening segment.