This invention provides a method for deactivating airborne microorganisms by providing required sufficient amount of chlorine dioxide into a space. This invention provides a method for deactivating airborne microorganisms in a space, the method contains (1): a step of providing a solid drug containing (A) a porous material contains chlorites and (B) a metal catalyst or a metal oxide catalyst, wherein, the mass ratio of the chlorites to the metal catalyst or the metal oxide catalyst is 1:0.04 to 0.8； (2): a step of exposing visible light to the solid drug； and (3): a step of providing a chlorine dioxide gas generated from the solid drug to a space where the airborne microorganisms exists.本發明提供一種對空間供給足夠需要的量之二氧化氯氣體，藉以使漂浮微生物失活之方法。本發明提供一種使空間中之漂浮微生物失活之方法，包含(1)：準備含有(A)載持有亞氯酸鹽之多孔質物質及(B)金屬觸媒或者金屬氧化物觸媒之固態的藥劑之步驟，在此，於前述固態的藥劑中之前述亞氯酸鹽與前述金屬觸媒或者金屬氧化物觸媒之質量比為1：0.04至0.8；(2)：對前述固態的藥劑，照射可見光之步驟；以及(3)：將從前述固態的藥劑所產生之二氧化氯氣體，供給於漂浮微生物所存在之空間之步驟。
