Abstract: A rear side door structure for four-door type automobiles including a rear door panel having an upper hem which defines a lower edge of a window opening, a guide member extending upwardly from the upper hem of the door panel to divide the window opening into a front opening portion and rear opening portion, a front glass panel fitted to the front opening portion, a rear glass panel disposed in the rear opening portion for movement along the guide member. The guide member is inclined rearwardly so that the rear glass panel is shifted forwardly when it is moved downwardly. According to this arrangement, the rear glass panel can be retracted into the door panel without any interference with the cut-off portion which is normally provided in the door panel at the rear lower portion for avoiding the rear tire house.