In this work, micro-sized particles of dextran, which has recently been focused as one of the candidate materials for the Drug Delivery System(DDS), were prepared by means of the Supercritical Antisolvent (SAS) process with CO2. With dimethyl sulfonate (DMSO) as the solvent, effects of the operating variables such as temperature (308.15K~323.15K), pressure (90bar~130bar), solute concentration ( 10 mg/ml~20 mg/ml), and the molecular weight of the solute(Mw=37,500, 450,000) on the size and morphology of the resulting particles were thoroughly examined. While the higher solute concentration resulted in the larger particles, the injection velocity of the solution and pressure did not show significant effects on the size of the resulting particles. For dextran of the lower molecular weight (Mw=37500), the smallest particle size was obtained at 313.15K. On the other, the size of the particles resulted from the high molecular weight dextran ranged between 0.1~0.5µm. Further, the higher temperature and pressure the larger the particles. For the solute concentration of 5 mg/ml, the lower molecular weight dextran did not form discrete particles while aggregation of the particles appeared when the solute concentration exceeded 15mg/ml for the higher molecular weight dextran. It is believed that if the solute concentration is too low, the degree of the supersaturation in the recrystallization chamber would not be sufficient for initiation of the nucleation and growth mechanism. Instead, the spinodal decomposition mechanism leads to formation of the island-like phase separation which appears similar to aggregation of the discrete particles. This effect would be more pronounced for the smaller molecular weight polymer system due to the narrower phase-splitting region.