OBJECTIVE To investigate the formation process and dynamic changes of important physical parameters of PLGA micro-sphere,
including particle size and its distribution, specific surface area. METHODS The double emulsification method was utilized to prepare the PLGA microsphere. The physical characteristics was determined with Malvern Mastersizer 2000. Macroscopic turbidity observation in suspension during double emulsification and the evaporation process of methylene chloride were also studied. RESULTS In the first 2 min, specific surface area increased with the rapid decreasing of particle size and the harmonization of particle size distribution. A good linear rela-tioaship was showed between the dynamic particle size change and stirring time. Afterwards these parameters were kept at constant level. No effect was found on the evaporation velocity of methylene dichloride from emulsion drops by the addition of PLGA. CONCLUSION The linear reduction in particle size, increasing in specific surface area and the uniformity of microsphere resulted in the rapid breaking up of emulsion droplets. While in the later phase, its further progression was inhibited by the increasing viscosity of dispersed phase due to the evaporation of organic solvent and increasing Young-Laplace force,so that the physical parameters were maintained at a relatively stable level.