To provide a building external wall moisture-proof sheet, a method for preventing dew condensation in a wall body using the same, and a wall structure having the external wall moisture-proof sheet attached thereto, by arranging a sheet having moisture-absorbing/ dehumidifying performance on an external wall of a venting layer of a building such as a house, to thereby quickly remove the moisture infiltrating into the interior of the venting layer, and by suppressing transfer of moisture into the wall (toward the moisture permeable waterproof sheet), to thereby suppress the high moisture inside the wall.

There is provide a sheet 1, 11 which is for use in a laminate on a side facing a venting layer of a building wall structure which consists of at least an external wall substrate, the venting layer, and an internal wall substrate superposed in this order from the outside. Moisture-absorbing/dehumidifying layers 5, 5' are superposed only on a single surface of each of moisture-proof resin sheet substrates 2, 7, and the moisture-proof resin sheets 1, 1' are superposed on the external wall side. Further, the moisture-absorbing/dehumidifying layers 5, 5' are placed on the venting layer 8 side. The thus laminated moisture-proof sheets 1, 1' are attached onto the side facing the venting layer 8 of the building external wall.