Cloud temperatures, phase behavior, and the structures of liquid crystals were investigated in the aqueous systems of homogenous hexaethylene glycol dodecyl ether(ClzE06) and tied C1~E04-C12EOs, C1~EO&~EOs, and C~ZEOO-C~ZEO~. In the mixed surfactant systems, the average polyoxyethylene-(EO-) chain lengths ate kept constant, the same as CIzE06. The change in cloud temperatures is small in all the systems, whereas the phase behavior is successively changed with increasing the difference in EOchain length in the mixture. Lamellar liquid crystal is developed in the phase diagmms and it intrudes in the two-phase region above the cloud temperature. Hence, the phase pattern of the present mixed surfactant systems resembles that of ClzEOs system, but both cloud point and W+L, region appear at much hi& temperature. Hence, the Hydrophile-Lipophile Balance of the surfactant is not largely changed by mixing the surfactants but the SAXS results show that the surfactant molecules are more tightly packed in the hexagonal and lamellsr phases by mixing. It is considered that when surfactants of different EO-chain lengths are mixed, the considerable reduction in repulsion between the hydrophilic moieties takes place and the surf-t molecules are more tightly packed.