An armrest for office chairs includes a pad and a sleeve coupled to the chair structure. A tray, having longitudinal strips with seats at their ends, is integral with the sleeve and houses a play recovery element having externally protruding appendages, and the play recovery element has two central curved portions with opposite concavities. The pad has two internally protruding bands, each having a central opening and forming end seats with the transverse edges of the pad; and a longitudinal relief with grooved side walls and two transverse ribs. The play recovery element has elastically inclined flaps and further has the appendages inserted into the seats of the tray. The side walls of the longitudinal reliefs engage the curved portions, and the two transverse ribs of the pad abut the inclined elastic flaps of the play recovery element to prevent the tray from disengaging when inserted into the pad.