Sulfamethizole was crystallized using both the supercritical and liquid antisolvent processes. Acetone and N,N-dimethyl formamide (DMF) were selected as solvents for the pharmaceutical compound, and carbon dioxide and distilled water were used as antisolvents. In the supercritical antisolvent process, the effects of experimental conditions such as carbon dioxide injection rate, type of solvent, and temperature were investigated. In the liquid antisolvent process, the effect of ultrasound on the properties of crystal was examined. The various crystal habits such as tabular, platy, acicular, and prismatic were observed depending on the process and experimental conditions. Differential scanning calorimetry (DSC) measurement revealed that the carbon dioxide injection rate affected the crystallinity of sulfamethizole particles. Larger crystals were obtained at higher temperatures in the two antisolvent processes. The particle size distribution was mostly affected by the antisolvent injection rate and the application of ultrasound. (C) 2003 Elsevier B.V. All rights reserved.