Porous polycarbonate membranes have been prepared using polycarbonate (PC) and polyethyleneglycol (PEG) in a reactor with supercritical CO₂. The porosity increased upon increasing the initial PEG concentration contained in the membrane from zero to 30 wt%. The inversion rate increased upon increasing the pressure in the range from 11 to 15 MPa and decreased upon increasing the pressure from 15 to 19 MPa. The inversion rate increased upon increasing the temperature from 30 to 45℃ and remained nearly constant at 98 wt% at temperatures over 45℃. Because the solubility of supercritical CO₂ was dependent on the pressure and temperature, the effects that the pressure and temperature had on the inversion rate were substantial. The inversion rate increased upon increasing the holding time from zero to 20 min and remained nearly constant at times over 20 min. The tearing stress of the membrane increased upon increasing the porosity and inversion rate.