The application of supercritical carbon dioxide (SCCO2) has been attracting more and more attention, especially in the formation of polymer membranes. The membrane formation using SCCO2 is analogous to conventional immersion precipitation process by using organic nonsolvent. Polylactide (PLA) membranes were prepared by phase separation with SCCO2 as nonsolvent. Two kinds of solvents were used to study the effect of the solvent on the cross-section structure of the PLA membrane and the compatibility between the solvent and SCCO2 was studied. The effect of the solvent and the preconditioning on the morphology of the PLA membrane was also investigated through scanning electron microscope, wide-angle X-ray diffraction, and polarizing microscopy. (C) 2004 Wiley Periodicals, Inc.