An adjustable spanner for quickly turning an object, comprising: a moving member; a first jaw adjustably jointed to the moving member; a second jaw cooperating with the first jaw; a grip having a first end grippable by a user, in use of the adjustable spanner and a second end opposite to the first end, with the moving member movably joined to the second end and movement thereof restricted by a first fastening device, with the first fastening device moveable in a slot (14; 14a) defined in the moving member and biased by an elastic member (15; 15a) disposed in the slot (14; 14a) and also fixed to the second end, with the second jaw pivotally joined to the second end by a second fastening device, with the second fastening device inserted in the second end and the second jaw, wherein the second jaw includes a guiding end including a side being in movable contact with an edge defined by walls of the moving member, the walls of the moving member forming a guiding channel; and wherein the adjustable spanner is able to be turned in a first direction that an object held between the first and second jaws (20, 30) is turned, with a relative position between the first and second jaws (20, 30) fixed, with a fixed first clamping distance defined between the first and second jaws (20, 30), and wherein the moving member is not moved relative to the grip; and wherein the adjustable spanner is able to be turned relatively to the object engaged therewith, with the adjustable spanner being turned in a second direction opposite to the first direction, and wherein the moving member moves relative to the grip, with the first jaw carried by the moving member to move away from the second jaw until the moving member and first fastening device stop, with a second clamping distance larger than the first clamping distance defined between the first and second jaws (20, 30) when the moving member stops, with the moving member being able to return to the relative position where the first and second jaws (20, 30) define the first clamping distance by the elastic member (15; 15a). a moving member; a first jaw adjustably jointed to the moving member; a second jaw cooperating with the first jaw; a grip having a first end grippable by a user, in use of the adjustable spanner and a second end opposite to the first end, with the moving member movably joined to the second end and movement thereof restricted by a first fastening device, with the first fastening device moveable in a slot (14; 14a) defined in the moving member and biased by an elastic member (15; 15a) disposed in the slot (14; 14a) and also fixed to the second end, with the second jaw pivotally joined to the second end by a second fastening device, with the second fastening device inserted in the second end and the second jaw, wherein the second jaw includes a guiding end including a side being in movable contact with an edge defined by walls of the moving member, the walls of the moving member forming a guiding channel; and wherein the adjustable spanner is able to be turned in a first direction that an object held between the first and second jaws (20, 30) is turned, with a relative position between the first and second jaws (20, 30) fixed, with a fixed first clamping distance defined between the first and second jaws (20, 30), and wherein the moving member is not moved relative to the grip; and wherein the adjustable spanner is able to be turned relatively to the object engaged therewith, with the adjustable spanner being turned in a second direction opposite to the first direction, and wherein the moving member moves relative to the grip, with the first jaw carried by the moving member to move away from the second jaw until the moving member and first fastening device stop, with a second clamping distance larger than the first clamping distance defined between the first and second jaws (20, 30) when the moving member stops, with the moving member being able to return to the relative position where the first and second jaws (20, 30) define the first clamping distance by the elastic member (15; 15a).