A length adjustable tool includes a first extending member including first and second ends thereof opposite to each other, with the first end thereof forming a first driving end. A second extending member includes first and second ends thereof opposite to each other, with first extending member slidably and non-rotatably engaged therewith, with the second end thereof forming a second driving end. A positioning mechanism engages with the first and second extending members and is operable to a first position in which the first and second extending members are stopped from sliding relative to each other and a second position in which the first and second extending members are slidable relative to each other.