The object of the present invention is to provide a package of a volatile substances which comprises a bag having a volatile substance with an antibacterial action enclosed therein, and a case having the bag enclosed therein, wherein the case is allowed to have a size and shape complying with the amount of a volatile substance having permeated the bag so that the shape of the case can be adapted to the volumes and shapes of various air conditioners, while the volatile substance can be volatilized at a predetermined rate. The package of a volatile substance according to the invention comprises a source generating the volatile substance, and a case which has the volatile-substance source enclosed therein and which has a wall at least a part of which is made of a gas-permeable resin, wherein the case is characterized in that a value expressed by the formula X×Z/Y is 200000 to 1500000 wherein X represents the surface area (mm2) of the wall; Y represents the thickness (mm) of the wall; and Z represents the vaporization amount (mg/day) of the volatile substance volatilized by the volatile-substance source per day in an atmosphere at 30° C.