A humidity-conditioning sheet 10 excellent in reversibility and responsiveness of a moisture adsorbing/desorbing ability of rapidly adsorbing moisture at high ambient humidity and conversely rapidly desorbing adsorbed moisture at low ambient humidity includes a sheet-shaped humidity-conditioning layer 7 formed by bonding together, with a thermoplastic resin powder 4, humidity-conditioning particles 3 which reversibly adsorb and desorb water vapor. The void ratio of the humidity-conditioning layer 7 is 5% or more. Since a ratio of voids 8 formed between the humidity-conditioning particles 3 is high, the voids 8 between the humidity-conditioning particles 3 can be used as water retention spaces for moisture adsorption and desorption, thereby achieving the high reversible moisture adsorbing/desorbing ability and excellent moisture adsorption/desorption responsiveness with the aid of not only the moisture adsorbing/desorbing ability inherent in the humidity-conditioning particles but also the moisture adsorbing/desorbing ability of the voids between the humidity-conditioning particles.