An aircraft engine pylon aft aerodynamic fairing includes upper spars, transverse stiffening ribs, lower spars and a trailing edge where the upper spars and lower spars join together. In this fairing, a profiled structure is formed according to a profile open to the outside of the fairing. In a first end portion, the profiled structure comes to be enclosed between an end portion of the lower spars and the ends of at least one transverse stiffening ribs flush with the lower spars. This structure extends between the lower spars and the upper spars over a straight central portion inclined relative to the first end portion, and comes in a second end portion flush against a portion of the upper spars, parallel to the first end.