A two step spray aerosol generator, named as filter expansion aerosol generator (FEAG), was introduced. The FEAG was composed of two-fluid nozzle for dispersing liquid, porous glass filter, and vacuum pump. Liquid is sprayed through a pneumatic nozzle by carrier gas on to a glass filter surface where it forms a thin liquid film. This liquid film and carrier gas pass through the filter pores by the carrier gas and expanded into a low pressure chamber. Mean droplet size was estimated to be 2.1 μm and standard deviation of the droplet size distribution was l.76. The FEAG process was applied to the production of many types of ceramic particles at low pressure by spray pyrolysis. The morphology of particles prepared by the FEAG process was different from those of ultrasonic spray pyrolysis. The potential applications of this spray generator will be film deposition and aerosol etching at reduced pressure.