An adjustable spanner, including a stationary jaw and a movable jaw, suitable to be coupled to the stationary jaw in a plurality of different positions in order to engage objects of different sizes, and adjustable coupling means provided between the stationary jaw and the movable jaw. The adjustable coupling means include a substantially flat base, which is fixed to said stationary jaw and which includes a folded portion laterally embracing the movable jaw, in such a way that the stationary jaw and the movable jaw lay substantially on the same plane.