To provide a moisture-conditioning building material board having a moisture-conditioning function, which is lightweight, free from fracture, and usable as an interior material for housing in Japan with a climate of high temperature and high humidity, by using a low-priced stoneware clay.

The moisture-conditioning building material board is manufactured by impregnating pores of an organic fiber porous body with a slurry of a solid concentration of 30-50 vol.%, where a mixed powder of slaked lime of 5-40 mass% and stoneware clay of 60-95 mass% is dispersed in water, drying and hardening by carbonation. It has a bulk specific gravity of 0.8-1.5, a bending strength of 2-9 MPa, and is not fractured even when it is bent up to 180°.