D-limonene in water nanoemulsion is prepared from an optimum formulation by low energy process at room temperature. The phase behavior of d-limonene/isotridecanol ethoxylate-6/ isopropyl alcohol /water system is systematically investigated to identify the optimum formulation. The microstructure of intermediate phases has been characterized by optical microscope and small angle X-ray diffraction. The microstructure of formulation concentrate has been further determined by means of electrical conductivity. The droplet size of nanoemulsion has been determined by light scattering and correlated with their microstructure. The results show that d-limonene nanoemulsion with droplet size of ca. 40 nm is obtained via the addition of the optimum formulation, which is a microemulsion, directly into water. This process involves composition change from a bicontinuous structure.