Water/CO2 (W/C) microemulsion was formed by sodium salt of bis(2,2,3,3,4,4,5,5-octa fluoro-1-pentyl)-2-sulfosuccinate and the phase behavior of this emulsion was investigated in supercritical state. In addition, the change of the phase behavior of W/C microemulsion was observed when various organic solvents were added into this microemulsion. The added organic solvents are isopropanol, n-propanol, ethanol, methanol, pyridine, 2-methoxyethanol, tetrahydrofuran, acetonitrile, acetone, and 1,4-dioxane. According to the results, the phase behavior of W/C microemulsion depended on the temperature and pressure and the microemulsion was thermodynamically stable in the special range of pressure. In case of W/C microemulsion with organic solvents, the phase behavior of this system was affected by the solubility parameter of organic solvents.