Objective: To optimize formulation of O/W microemulsion of Saussurea involucrate. Method :Both chlorogenic acid and rutin used as indexes

solubility in various solvents of extracts from S. involucrate was determined by HPLC

and obtained primary compositions of microemulsion formulation

formulations of S. involucrate microemusion was optimized by practicing pseudoternary phase diagram and determined its quality including viscosity

conductivity

refractive index

zeta potentia

particle size distribution respectively. Result :Maximum area of microemulsion in pseudo-ternary phase diagrams was obtained when Km was 1 ∶2. Optimum microemusion formulation was RH 40 as surfactant

alchol as cosurfactant and oleic acid as oil phase with its proporation as 4 ∶2 ∶1. Viscosity and mean particle size of S. involucrate microemulsion accorded with requirement of transdermal microemuslion.It was stable under high temperature and strong light condition(non-hierarchical

non-flocculation or precipitation of drug). Conclusion: Solubility of extracts from S. involucrate was improved by microemulsion. This microemulsion had characteristics of small particle

stability and suitable viscosity etc.