At a back door structure, a back door, that is rotatably supported at a rear roof header via a pair of door hinges, rotates around hinge shafts and opens and closes a rear opening portion. The back door is held in a fully open posture that opens the rear opening portion, by a single damper that is provided only at a right side with respect to the rear opening portion. In the back door structure, a fit posture of the back door is corrected due to a vertical position of a mounting surface of the door hinge at the right side being set at an upper side with respect to a mounting surface of the door hinge at a left side in a state of not supporting the back door.