PURPOSE: To provide humidity conditioning material for use in a sealed container or a room, building etc., which maintains constant the humidity of air in a container etc., by impregnating a porous siliceous substance with an aqueous solution of a water-holding agent, drying, and maturing it.

CONSTITUTION: A siliceous substance is impregnated with an aqueous solution of water-holding agent to be coated therewith and dried. The dried matter is left as it is in a sealed space above a saturated solution of salts having certain vapor pressure or in a constant-humidity, constant temperature tank of steam humidification type to be matured and then housed in a steam- permeable container to obtain a humidity conditioning material. As a water- holding agent, methyl cellulose, ethyl cellulose, polyvinyl alcohol etc., are used. As a porous siliceous substance, zeolite, bentonite, terra abla, diatomaceous earth etc., are used. The humidity conditioning material is used by placing it in an air-permeable container having holes in part or a container made up of steam-permeable but liquid-impermeable films.