The objective of this study was to find the effect of the initial droplet size in the ASES (aerosol solvent extraction system) process. We prepared poly(L-lactic acid) (PLLA) nano- and micro-particles using ASES process. The experiments were carried out on various conditions. We got PLLA particles that had mean particle diameter from 0.54 to 1.28 mu m. And we calculated theoretical initial droplet size with the equation derived by Lorenzetto and Lefebvre and investigated the relation between the initial droplet size and particle size. The results show that there is a linear relationship between the initial droplet size and particle diameter.