A synthetic glucolipid, 1,3-di-O-phytanyl-2-O-(beta-glucosyl)glycerol in water was examined by small-angle X-ray scattering, differential scanning calorimetry, and polarizing microscopy. These measurements showed that the aqueous lipid forms an Fd3m reverse micellar cubic phase (lattice constant = 148 Angstrom) over a wide temperature range (at least from -20 to 80 degrees C). The X-ray scattering revealed that the phase structure is stable at 0 and 25 degrees C for months without any detectable chemical change. For the fully hydrated cubic phase, its hydration amount was determined to be 4.4 mol/mol (water/lipid) by calorimetry at 0 degrees C. From these experimental values, the structural parameters of the cubic phase were evaluated on the basis of the proposed structure model. The evaluation is compared with the molecular dimensions of the glucolipid.