An adjustable automatic positioning hinge for a glass door includes a doorframe mount, a body, a spindle, a positioning device, a door bracket and two adjusting screws. The body is attached to the doorframe mount and rotatably holds the spindle. The spindle has an exterior surface and two inclined adjusting flats defined in the exterior surface. The positioning device is mounted in the body to position the spindle. The door bracket holds the spindle and clamps a glass panel. The adjusting screws are mounted in the door bracket and respectively have an inside end abutting the corresponding inclined adjusting flat. Consequently, the adjustable hinge is simple, and small adjustments can be made to align the glass panel with a doorframe of the glass door.