Spherical shape cobalt oxide powders with fine size were directly prepared by spray pyrolysis using a filter expansion aerosol generator (FEAG). These cobalt oxide powders were then compared with the powders prepared by ultrasonic spray pyrolysis. The cobalt oxide powders prepared using a FEAG are finer and have more narrow size distribution and filled morphologies than those prepared by ultrasonic spray pyrolysis. The mean sizes of the cobalt oxide powders prepared using a FEAG increased from 230 to 860 nm when the concentration of the spray solution was increased from 0.01 to 2 M.