Microemulsion is prepared by the method of phase inversion emulsification with d-limonene that is environmental friendly substance and nontoxic to human body as dispersed phase. Emulsifier used for preparation of microemulsion is nonionic surfactants, polyoxyethylene nonylphenyl ether. Stability of prepared microemulsion was estimated by the various method of ξ-potential, hydrodynamic diameter and electric conductivity. When d-limonene is emulsified by NP series, microemulsion is most stable and narrowly distributed at HLB value of 12.3(either one emulsifier or mixed emulsifiers). Stability of microemulsion is increased as the amount of emulsifiers is increased at same HLB value of 12.3. In the case of using the same amount of emulsifiers, number of produced micelle are relatively large as hydrodynamic diameter is small. Therefore, the state of microemulsion is stable and the electric conductivity is increased. One can determine that higher electric conductivity value means that microemulsion has more micelles and is more stable.