To provide a seat back carpet mounting structure capable of preventing the whole carpet from appearing levitated, performing easy location of boards and simple and quick assembling operations, precluding deformation of flexible part(s), and enhancing the appearance of the rear face of the seat back.

The carpet 13 is attached to boards 15 and secured to frames 12 of a left and a right seat back 11.... A space part 25 is formed at the adjoining side ends 15a of the left and right boards 15. The lateral edges 13a of the carpet 13 are included in winding to the rear surfaces space part of the boards in such a condition as protruding outward laterally from the side ends 15a of the boards 15 in such a way filling the space part 25, and a flexible part 13b free of board 15 is formed at each lateal edge 13a of the carpet 13. Each flexible part 13b is furnished with a sewing part 31 stretching in the vertical direction.