Supercritical CO 2 is an attractive green solvent. [1] However, CO 2 is generally a poor solvent for high-molecular-weight or hydrophilic molecules, which rules out many potential applications. An effective way to solve this problem is to create reverse micelles or microemulsions with supercritical CO 2 as the continuous phase. Many studies have been carried out on water-in-CO 2 microemulsions and reverse micelles in supercritical CO 2 with water domains. [2] Researchers have also investigated the applications of water-in-CO 2 microemulsions, for example, for the extraction of biomolecules [2c,d] and metal ions, [3] for the preparation of nanoparticles, [4] and as media for chemical reactions. [5] Room-temperature ionic liquids, which are organic salts with melting points below 100 8C, have attracted much attention. [6] They can dissolve many organic and inorganic substances, and their properties are tunable to satisfy the requirements of a variety of tasks. Many ionic liquids can be considered as cleaner solvents than standard solvents because they are nonvolatile and often nontoxic or low toxic. Ionic liquids have potential applications in a range of areas, such as separations, [7] chemical reactions, [8] and materials synthesis. [9] It was reported that ionic liquids could dissolve supercritical CO 2 , whereas the solubility of ionic liquids in supercritical CO 2 was negligible. [10] Very recently, reverse micelles with ionic-liquid cores have attracted much interest, [11] and a variety of reverse micelles with organic solvents [11a,b] and with water [11c] as the continuous phase have been studied. The combination of supercritical CO 2 and ionic liquids is interesting from academic, environmental, and practical points of view. The creation of reverse micelles in supercritical CO 2 with ionicliquid domains is certainly a very interesting topic: Ionic liquids can be dispersed in supercritical CO 2 , and the systems may combine some advantages of the two fluids. Herein, we report our findings that N-ethyl perfluorooctylsulfonamide (C 2 H 5 NHSO 2 C 8 F 17 ; N-EtFOSA) can form reverse micelles in supercritical CO 2 with 1,1,3,3-tetramethylguanidinium ([(CH 3 ) 2 N] 2 C=NH 2 + ) acetate (TMGA), 1,1,3,3-tetramethyl-[