It was found that Dynol-604, a non-fluorous and no silicon-containing nonionic surfactant, was soluble in supercritical (SC) CO2. The phase behavior of SC CO2/Dynol-604/water system was studied. The results showed that one-phase water-in-CO2 microemulsions could be formed. The solubilization of methyl orange in the microemulsions proved further the existence of water domain in the microemulsions. It was found that Dynol-604, a non-fluorous and no silicon-containing nonionic surfactant, was soluble in supercritical (SC) CO2. The phase behavior of SC CO2 / Dynol-604 / water system was studied. -phase water-in-CO2 microemulsions could be formed. The solubilization of methyl orange in the microemulsions proved further the existence of water domain in the microemulsions.