Objective: To study the characteristics of particle size distribution in O/W microemulsion gel and its difference from hydrogel. Method: The diluted O/W microemulsion gel was detected by using dynamic light scattering. The pretreatment methods and conditions of sample were investigated to determine its detection method;Average size of microemulsion gels with different gel matrix and different microemulsion formulae were tested

which can be used to compare with hydrogel. Result: The result showed that average size of O/W microemulsion gels can be determined after being diluted 100 times. Its average particle size was between 10 nm and 100 nm.The size distribution of microemulsion gel is similar to the same formulae of microemulsion

which was obviously different from hydrogel. Conclusion: Size measurement can be used as a testing index for microemulsion gel.