Abstract: According to a generator for producing a narrowly size-distributed aerosol, the solution is atomized into the first droplets including a predetermined small-sized range of droplets by the atomizer, and then using the droplet depositor, the larger droplets from the predetermined small-sized range of droplets are deposited in the first droplets, and wherein the second droplets are formed from the first droplets, and then a particulate screening and separating device is used to extract the third droplets smaller than the predetermined small-sized range of droplets within the second droplets, and the predetermined small-sized range of droplets can be obtained thereof. Therefore, a aerosol generator can function as a device characterized with the alternative distributions of a narrowly size-distributed aerosol with high concentration in mass, and the liquid or solid aerosol can be generated thereof. The Geometric Standard Deviation (GSD) of the droplet size distribution can be kept under 1.