We investigated the structure and formation process of lamellar domains below the Krafft temperature in two nonionic surfactants, the C16E7/water and C16E6/water systems, using an optical microscope and small-angle X-ray scattering. We found that vesicles and long leek-like lamellar domain structures are formed in the C16E7 and C16E6 systems, respectively. This large difference between the lamellar domain structures of the systems can be explained by the elastic properties of bilayers in the structural formation process.