A ratchetable open-ended wrench includes a handle for a hand to grasp, a wrench head located on one end of the handle, and a fastener room located in the wrench head for accommodating a workpiece to be rotated. The wrench head further includes a first jaw having a first driving wall, a second jaw having a second driving wall facing the first driving wall, an inner wall extending from the second driving wall into the second jaw, a concavity, an auxiliary jaw retracting opening, an auxiliary jaw capable of longitudinally sliding into the auxiliary jaw retracting opening in an elastic way, and an auxiliary jaw limiting member coupled to a limiting slot. The auxiliary jaw further includes an exterior end having a pillow in contact with the driving wall and a pushing surface for working together with the first jaw to grip the workpiece under operation, an interior end, and a limiting slot.