Middle-phase microemulsion (surfactant phase) is formed in a water/sucrose monododecanoate (SE)/hexanol/decane system, Based on the geometrical relations of a particular three-phase triangle in the quaternary system, the monomeric solubility of hexanol in the excess oil phase and the mixing fraction of SE and hexanol at the water-oil interface inside the microemulsion were obtained, Both values are almost unchanged with increasing temperature, This phase behavior is completely different from that for a system including an ordinary polyoxyethylene-type nonionic surfactant and resembles that in a brine/ionic surfactant/cosurfactant/oil system, On the other hand, the solubilization capability of the SE-hexanol mixtures decreases at higher temperatures due to the decrease in the compatibility of the microemulsion with oil, However, the mixing ratio of mixed surfactant for the maximum solubilization is not greatly changed, Consequently, temperature-insensitive microemulsions can be attained in the present SE system, The effect of oil or surfactant chain length on the phase behavior is also discussed.