The morphological and structural characteristics of aqueous sodium dibutyl phosphate (DBP) have been investigated at all levels from molecular to superstructural by using polarized microscopy, light scattering, small-angle X-ray scattering, and nuclear magnetic resonance techniques. Above a certain concentration, the aqueous solutions separated into two liquid phases, one of which was spontaneously birefringent. The birefringent phase first separated in the form of spherulites, in which the hydrocarbon chains are oriented parallel to the radial direction. With increasing concentration, a transition from spherulitic to rodlike texture occurred and the system finally became a continuous birefringent phase. The spherulitic and/or rodlike textures were gradually destroyed with increasing temperature and disappeared at 55 degrees C. However, the X-ray scattered intensity distribution indicated that despite the disruption of superstructures at 70 degrees C, the bilayer blocks (assemblies) are maintained without separating into bilayer micell units which can be regarded as two weakly interacting monolayer composed of DBP. Above a critical concentration, the longitudinal and transverse relaxation times predicted that the motion of carbons is strongly restricted by hydrocarbon chain interaction.