We clarified the generation mechanism of defects appearing on the surface of electroceramic green bodies after the selective removal of plasticizer using supercritical carbon dioxide. First, we developed a supercritical in situ observation system. The density of defects on the surface of the green bodies increased not only during the pressurization step but also during the depressurization step. A simple system comprising only the plasticizer and supercritical carbon dioxide was used in combination with a novel capillary glass tube method for the investigation. The relative volume of the plasticizer increased with increasing pressure and reached its maximum of 1.25 at 8 MPa. The bubbles formed inside the plasticizer during the depressurization step because the carbon dioxide dissolving in the plasticizer was not solvated any further at lower pressures. We concluded that the increase of volume and bubble formation in the plasticizer are the primary causes of the surface defect generation on the green bodies treated with supercritical carbon dioxide. To eliminate generation of the surface defects on the green bodies, the increase of plasticizer volume caused by carbon dioxide dissolving in the plasticizer must be suppressed, and the dissolution of the plasticizer in carbon dioxide must be simultaneously enhanced. (C) 2003 The Electrochemical Society.