This research aims at developing the moisture exhaust exterior wall which can discharge indoor humidity to the outdoor air by using a part of exterior wall as the monolayer wall of the humidity control building materials which have permeability. Indoor humidity can be naturally discharged using the water-vapor-pressure difference between the indoor air and the outdoor air in winter. In this paper, the reduction effect of indoor relative humidity is shown based on the experimental result which used the climate chamber. The building-material load factor and the moisture exhaust slope were specified as indexes showing the performance of the moisture exhaust exterior wall. Since the relation between the building-material load factor and the time required for specific reductions in indoor relative humidity was analyzed, and selection of a building-material load factor corresponding to the house conditions was possible.