The invention concerns a foldable seat (1) for a rollator or a wheelchair,saidseat comprising:- a first rigid plate (2) and a second rigid plate (3), said plates beingadjacentlyconnected along a longitudinal axis (XX') so as to be rotatably moveablearoundsaid longitudinal axis (XX') between an unfolded position, in which theirplanesurfaces (2a, 3a) are approximately aligned, and a folded position, in whichtheirplane surfaces (2a, 3a) define an angle less than 1800, and preferably, anangleapproximately equal to zero, said plates (2, 3) being also configured so as tobepivotally connectable to a frame of a rollator or a wheelchair, and- a hinge (10) pivotally connecting said first plate (2) to said second plate(3),wherein said hinge (10) comprises at least a first cylinder (11) integral withsaidfirst plate (2), said first plate (2) projecting over said first cylinder(11), at least asecond cylinder (12) integral with said second plate (3), said second plate(3)projecting over said second cylinder (12), and a pivot pin (14) extendingthroughaxial through-bores and/or apertures (11c, 12c) of said first and secondcylinders (11, 12), said pin (14) defining said longitudinal axis (XX'),wherein said seat (1) further comprises a locking/unlocking system (20)configured to be actuated by hand by the user so as to lock, respectivelyunlock, said first and second plates (2, 3) into, respectively from, saidunfoldedposition and/or said folded position, said locking/unlocking system (20) beingatleast partially lodged inside said first and/or said second cylinder (11, 12).
