A ventilation sheet is installed between a seat pad and a skin that form a seat of a vehicle. The ventilation sheet includes a ventilation sheet main body formed in a thin plate-shape including an air flow passage through which an air flow flows, a plurality of openings in communication with the air flow passage of the ventilation sheet main body, the plurality of openings formed to open at a surface of the ventilation sheet main body facing the skin, and a connection passage in communication with the air flow passage of the ventilation sheet main body and in communication with a pad hole provided in the seat pad.