A phase transition from a lamellar liquid crystal to a middle-phase microemulsion (or surfactant phase) takes place with decreasing surfactant content in the water/sucrose monododecanoate/hexanol/decane system. Considering the monomeric solubility of hexanol in oil, the phase transition from the lamellar liquid crystal to a microemulsion was investigated at equal weight ratio of water and decane by a phase behavior study, small-angle X-ray scattering, and electron spin resonance spin-probe methods. In this system, the interlayer spacing of the lamellar liquid crystal, d, gradually increases upon addition of water and oil. The hexanol molecules are distributed between the palisade layers and the oil core in the lamellar liquid crystal. The bilayer becomes more flexible upon dilution and, eventually, the lamellar liquid crystal changes to a bicontinuous microemulsion. The surfactant weight fraction at the microinterface inside the bicontinuous microemulsion is also discussed.