Micronized camptothecin (CPT) is prepared with a supercritical antisolvent (SAS) apparatus using dimethyl sulfoxide (DMSO) as solvent and carbon dioxide as antisolvent. Four factors, namely CPT solution concentration and flow rate, precipitation temperature and pressure are optimized by a four-level orthogonal array design (OAD). By analysis of variance (ANOVA), only precipitation pressure has a significant effect on the MPS of micronized CPT. The optimum micronization conditions are determined as follows: CPT solution concentration 1.25 mg/ml, CPT solution flow rate 6.6 ml/min, precipitation temperature 35 degrees C and precipitation pressure 20 MPa. Under the optimum conditions, micronized CPT with a MPS of 0.25 +/- 0.020 mu m is obtained. The micronized CPT obtained was characterized by Scanning Electron Microscopy (SEM), Atomic Force Microscope (AFM), High performance liquid chromatography-mass spectrometry (LC-MS), Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), Differential scanning calorimeters (DSC) and Gas chromatography (GC) analyses. The results showed that the obtained CPT particles have lower crystallinity and SAS micronization process does not induce degradation of CPT. In addition, the residual DMSO is less than the ICH limit for class 3 solvents. (C) 2009 Elsevier B.V. All rights reserved.