Ester based anionic surfactant-sodium lauryl sulfoacetate (SLSA)-is one of the most important surface-active ingredients in several personal care products however no scientific report is available regarding its lyotropic and thermotropic phase behavior in water. In the present study, SLSA and its congener sodium myristyl sulfoacetate (SMSA) are investigated for their self-aggregation properties in aqueous system. Phase transition temperature of these surfactant-water mixtures is determined by differential scanning calorimetry (DSC). Their lyotropic and thermotropic phase behavior in water are investigated by polarized optical microscopy (POM), small-angle X-ray scattering (SAXS) and wide-angle X-ray scattering (WAXS). These surfactants predominantly exist as different types of self-assembled lamellar phases along with or without solid crystalline phases in aqueous system.