Ionic liquids (ILs), representing no measureable vapor pressure, have been proved to be useful as a replacement for ordinary organic solvents to reduce volatile organic compound (VOC) emissions. However, most of hydrophilic substances such as proteins, and catalysts are insoluble in most ILs. This limitation was overcome by the formation of nanometer-sized water domains in a hydrophobic IL [C₈mim] [Tf₂N] (1-octyl-3-methyl imidazolium bis(trifluromethyl sulfonyl) amide)  stabilized by the layer of anionic surfactant sodium bis(2-ethyl-1-hexyl) sulfosuccinate (AOT) in the presence of 1-hexanol as a cosurfactant.  The phase behavior of the AOT/water/IL system, dynamic light scattering study and solvatochromic probe study demonstrated the existence of water domains in the IL microemulsions. We tested the solubility of various enzymes and proteins in IL and in water-in-IL microemulsions. The results show that the microemulsions can solubilize enzymes and proteins, whereas IL alone or water saturated IL can not solubilize such biomacromolecules. The catalytic activity of one of the enzymes (lipase PS) dissolved in the water domains of IL became much higher than in microemulsions of AOT in isooctane. Therefore, this work opens up new possibilities for biocatalytic reactions in ionic liquids, which are receiving increasing attention as "green" solvents for organic synthesis and catalytic processes.