Objective: To optimize preparation prescription of Bushen Wenfei microemulsion oral liquid. Method: Microemulsion prescription was optimized by pseudoternary phase diagram method

particle size was measured

transmission electron microscopic view was observed

and initial physical stability of microemulsion were investigated. Result: Optimum prescription was:volatile oil from Atractylodes macrocephala

Saposhnikovia divaricata and Asarum sieboldii as oil phase

extraction concentration liquid(3 g·mL-1) of Epimedium brevicornum

Astragalus membranaceus and Cornus officinalis as water phase

Tween-80 as surfactant

ethanol as cosurfactant. Electron microscope view showed microemulsion was spherical

average particle size was (18.25±0.08) nm

average PDI was 0.212±0.02

physical stability of prepared microemulsion was good. Conclusion: Volatile oil from the prescription could be oil phase to form microemulsion

particle size of prepared microemulsion distributed uniform with stable nature.