Phase behavior of aqueous mixture of imidazolium ionic liquid, 1-dodecyl-3-methylimidazolium bromide, was investigated by means of differential scanning calorimetry and polarized optical microscopy. The mixture forms two types of lyotropic liquid-crystalline gels, one is composed of lamellar phase and the other is of hexagonal phase. T-X phase diagram of the mixture was constructed, which defines the regions of various phases appearing in this mixture. (c) 2006 Elsevier Inc. All rights reserved.