A medium voltage vacuum contactor comprising for each pole, a vacuum envelope which contains a fixed contact and a corresponding movable contact; and actuating means providing the energy required to move the movable contacts, characterized in that said actuating means comprise an electromagnetic actuator having: a magnetic yoke which has an inner cavity communicating with the outside through at least a first opening; at least one coil accommodated in the cavity; a movable armature which is operatively connected to at least one movable contact through coupling means, and is mounted axially displaceable in the cavity with at least one end protruding from the first opening; at least one permanent magnet devoted to directly hold the movable armature in two stable positions. Further, there are provided means for guiding the movement of the movable armature which are positioned outside the yoke in correspondence of at least the first opening.