An automotive vehicle has a single integral door opening on each side of the door body. The door opening is closed by a pair of front and rear doors which are slidable along the vehicle side to open and close the door opening. The rear edge of the front sliding door and the front edge of the rear sliding door directly oppose each other without a vehicle body pillar therebetween. The opposing edges of the sliding doors have seals for water-proofing. Also, the upper edges of the sliding doors sealingly contact seals mounted on vehicle side frames extending along upper edge of the door opening for water-proofing. Guide rails slidingly supporting the sliding doors are mounted on the side frames in such a manner that they serve to reinforce the side frames. Lower seals are provided between the lower edges of the front and rear doors and the lower side frames for establishing water-tight seal therebetween.