Prefabricated piece of concrete with drainage and aeration system to protect against erosion by water currents. Piece (1) prefabricated concrete with a footprint (2) and a lower surface (3) converging towards a first base (4), a riser (5) parallel and greater, and both sides (6) parallel, comprising a chamfer (7) between the tread (2) and the riser (5), and where the drainage and aeration system comprises at least three longitudinal conduits (8) and a horizontal transverse conduit (9), parallel to the first and second bases ( 4, 5) and arranged on the center of gravity of the piece, from a recess (10) in one of the sides (6) to a recess (10) in the side (6) parallel, where the longitudinal conduits (8) they have a first end (8.1) of entry located in the chamfer (7) and a second end (8.2) that connects with the transverse conduit (9). (Machine-translation by Google Translate, not legally binding)