The lamellar liquid crystalline phases composed of either imidazolium salt, the hydrophilic 1-butyl-3-methylimidazolium tetrafluoroborate (bmim-BF 4 ) or the hydrophobic 1-butyl-3-methylimidazolium hexafluorophosphate (bmim-PF 6 ), in aqueous solution of Brij-30 (tetraethylene glycol lauryl ether, C 12 E 4 ) have been assembled at a constant temperature (T=25°C). Their elaborate structures such as the distribution of hydrophobic or hydrophilic parts of surfactant bilayer and water are revealed quantitatively by several structural parameters derived from small-angle X-ray scattering (SAXS) measurements. The effects of system composition and temperature on the lamellae are discussed with comparison to the corresponding Brij-30/water binary mixture. It concludes that the bmim-PF 6 molecules tend to situate at the interface between polar and apolar regions and therefore cause a decrease of combined water amount around EO blocks. Bmim-BF 4 molecules, however, like to locate themselves at water interlayers as well as in the polar domains. In addition, the pseudo-hexagonal columnar structures or micelles observed respectively at low or high temperatures are analyzed by SAXS and differential scanning calorimetry (DSC) methods.