Abstract: Process and device for continuously pickling at least one of the sides of a substrate (1), according to which this substrate (1) is moved according a predetermined direction between an anode (8), with respect to which it is polarised negatively, and at least one magnetic circuit (2) disposed opposite this anode (8), the side to be pickled being directed towards the anode (8), and, in the proximity of this side, a plasma (10) is created in a gas so as to generate radicals and/or ions acting thereon, use being made of means enabling to adjust the width of the field of action of the magnetic circuit to the width of the zone of the substrate (1) which is to be pickled.