Face protection accessory for helmets, in particular work or sports protective helmets, comprising: at least one support structure having two engagement portions for its engagement to an outer surface of a helmet; at least one transparent or perforated face protection structure, to allow a user wearing said helmet to see through the latter, said face protection structure being engageable to said support structure to form said face protection accessory and is removable from said support structure to remove said face protection structure from the helmet or to replace said face protection structure with another different face protection structure; coupling means operatively interposed between said at least one support structure and said at least one face protection structure, said coupling means being switchable between a first condition, in which they maintain said support structure and the respective face protection structure mutually engaged, and a second condition, in which they do not maintain said support structure and the respective face protection structure mutually engaged, these latter being separable, said coupling means comprising at least two coupling seats each obtained at opposite ends of an engagement edge of said face protection structure and at least two coupling pins each moveable preferably independently from the other between a first position, in which it does not engage the respective coupling seat of said face protection structure, and a second position, in which it is inserted in the respective coupling seat of said face protection structure so that it cannot move with respect to said support structure, each coupling pin being rotatably moveable between the first position and the second position, characterized in that each coupling pin comprises: at least one hollow cylindrical body fitted on a cylindrical support projecting from said support structure, said hollow cylindrical body rotating on the respective cylindrical support of said support structure about its own longitudinal axis; at least one coupling portion transversely projecting from said hollow cylindrical body and circularly developing about the latter according to a predetermined circular sector, the coupling portion of each coupling pin of said coupling means inserting into and removing from the respective coupling seat of said face protection accessory through the rotation of the hollow cylindrical body on said cylindrical support of said support structure. at least one support structure having two engagement portions for its engagement to an outer surface of a helmet; at least one transparent or perforated face protection structure, to allow a user wearing said helmet to see through the latter, said face protection structure being engageable to said support structure to form said face protection accessory and is removable from said support structure to remove said face protection structure from the helmet or to replace said face protection structure with another different face protection structure; at least one hollow cylindrical body fitted on a cylindrical support projecting from said support structure, said hollow cylindrical body rotating on the respective cylindrical support of said support structure about its own longitudinal axis; at least one coupling portion transversely projecting from said hollow cylindrical body and circularly developing about the latter according to a predetermined circular sector, the coupling portion of each coupling pin of said coupling means inserting into and removing from the respective coupling seat of said face protection accessory through the rotation of the hollow cylindrical body on said cylindrical support of said support structure.