Provided is a method of producing an inorganic fiber mat, the method enabling efficient adhesion of an aldehyde scavenger to an inorganic fiber mat while preventing the aldehyde scavenger from scattering around. The method of producing an inorganic fiber mat includes a fiber collection step of applying a binder to inorganic fibers and accumulating in a mat-like shape on a conveyor line to form an inorganic fiber web, a binder-curing step of heat-curing the binder applied to the inorganic fiber web to form an inorganic fiber mat, and an aldehyde scavenger application step of applying an aldehyde scavenger to the inorganic fiber mat, in which the aldehyde scavenger application step involves spraying the aldehyde scavenger in a form of droplets having an average diameter of 1 to 50 μm on a front side of the inorganic fiber mat and sucking from a back side of the inorganic fiber mat.