An adjustable wrench includes two walls disposed on an upper portion of a handle body to define a transversely extending guiding slot therebetween. A driving shaft is rotatably mounted in the guiding slot. Two movable jaws have coupling portions which are coupled respectively to two connecting ends of the driving shaft by force transmitting mechanisms such that a rotational force of the driving shaft about a rotating axis is transmitted to drive the coupling portions to move along the rotating axis toward or away from each other, and two jaw portions which extend outwardly of the guiding slot for gripping a torqued object. By operating a middle portion of the driving shaft, the distance between the jaw portions can be adjusted to permit quick gripping and releasing of the torqued object.