[Problem] To provide a method for inactivating airborne microorganisms by supplying a sufficient amount of chlorine dioxide gas into the air. [Solution] Provided is a method for inactivating airborne microorganisms which includes: (1) a step in which a solid chemical agent is prepared, said solid chemical agent containing (A) a porous material supporting a chlorite and (B) a metal catalyst or a metal oxide catalyst, such that within the solid chemical agent, the mass ratio of the chlorite to the metal catalyst or the metal oxide catalyst is 1:0.04-0.8； (2) a step in which the solid chemical agent is exposed to visible light； and (3) a step in which chlorine dioxide gas produced from the solid chemical agent is supplied into air containing airborne microorganisms.
