The phase behavior of the ternary system consisting of ethylene glycol (EG), 1-butyl-3-methylimidazolium hexafluorophosphate ([Bmim][PF 6 ]), and TX-100, was determined at 30.0°C. It was demonstrated that there were a single-phase region and a two-phase region in the ternary phase diagram. The single-phase region could be further divided into [Bmim][PF 6 ]-in-EG, bicontinuous, and EG-in-[Bmim][PF 6 ] microemulsion regions by conductivity. The microemulsions were characterized further by dynamic light scattering (DLS), freeze-fracturing electron microscopy (FFEM) and UV–vis spectrophotometry, indicating the microemulsion formation with spherical droplets and the formation mechanism similar to the common microemulsions.