Abstract: Properties of mixed aqueous solutions of ionic liquid (\Cnmim\Br) and traditional surfactant (SDS) were studied. Results showed that the properties of the mixed systems varied with the chain length of substituted alkyl in ionic liquids. Only those systems containing ionic liquids with equal to or more than 6 carbon atoms in alkyl chains can form aqueous two phase system (ATPS). The ATPS containing ionic liquids and surfactant has obvious extraction ability to xylenol orange and the potential to separate and purify biomaterials. The difference in appearance of ATPS should be attributed to the various size and shape of the surfactants aggregates formed in mixed solutions. Furthermore, the electrostatic attractive interaction，the hydrophobic interaction in addition to the synergistic effect between ionic liquids and SDS further promote the surfactant assembly, which leads to the formation of liquid crystal at lower surfactant concentration.