An adjustable dismantling tool for annular member is provided. A handle has opposing first end and second end and an axial direction passing through the first and second ends. A first main body is disposed at the second end and radially unmovable relative to the axial direction. A second main body is rotatably assembled with the first main body, radially unmovable relative to the axial direction and radially formed with a plurality of guiding troughs relative to the axial direction. Each of movable members has a guiding block slidably disposed in corresponding guiding trough. Each of connecting arms is disposed between the first and second main bodies, pivoted to the first main body and one of the guiding block to respectively form a first pivoting portion and a second pivoting portion, and swingable about the axial direction with the first pivoting portion as the center.