An adjustable wrench includes a fixed jaw, a movable jaw, and a handle, and a lock mechanism. The fixed jaw includes an adjusting mechanism and an abutting mechanism disposed therein. The adjusting mechanism includes a worm gear, with the worm gear rotatable about and movable along a fixing member. The abutting mechanism includes an abutting member pivotally fixed and including an end engagable with the worm gear. The movable jaw is engaged with the worm gear and moves linearly relative to the fixed jaw upon rotating the worm gear. The handle is pivotally fixed to the fixed jaw. The lock mechanism is installed between the fixed jaw and the handle and operable to a lock position a relative pivotal movement between the fixed jaw and the handle is obstructed and to an unlock position the fixed jaw and the handle are able to pivot relative to each other.