A new kind of biamphiphilic ionic liquid (BAIL) consisting of 1-dodecyl-3-methylimidazolium (C(12)mim(+)) and dodecyl sulfonate (DSN-) has been synthesized and characterized for the investigation on its self-assembling behavior with beta-CD in the aqueous medium. Vesicles were found in the diluted C(12)mimDSN@3 beta-CD solution, and on increasing the concentrations of both IL and beta-CD, the solution turned into a white hydrogel, which showed a temperature-dependent sol-gel transition. The building block consisting of one C(12)mimDSN and three beta-CDs was proposed, and a novel self-assembly mechanism was studied. Both cation and anion of the BAIL are involved in the self-assembling with beta-CD. The electronic interaction between C(12)mim(+) and DSN-, the hydrophobic interaction between the alkyl chains of BAIL and beta-CD cavity, H-bond between neighboring beta-CDs, and the interaction between imidazolium headgroup and water in the hydrogel are the driving force for