Abstract: The purpose of this study was to prepare compound rifaximin nanoemulsion and to analyze its physical and chemical properties.Using the drug loading capacity and stability of nanoemulsion as evaluating indexes,the oil phase,surfactant and co-surfactant were selected;the optimum formula was designed using pseudo-ternary phase diagram;the micromorphology and particle size of the nanoemulsion were observed and determined by transmission electron microscopy and laser particle size analyzer,respectively;the type of nanoemulsion was identified by staining test;the stability of nanoemulsion was investigated by light test,temperature test and high-speed centrifugation test.The results showed that the optimal formula of the compound rifaximin nanoemulsion was rifaximin 1%,cinnamaldehyde 2.44%,polyethylene glycol-200 4.88%,polyoxyethylene ether-40-castor oil 19.51%and distilled water 72.17%;the compound rifaximin nanoemulsion was oil-in-water(O/W)type and could be diluted infinitely;under transmission electron microscope,the nanoemulsion particle was spherical and had no adhesions,with the average particle size of 11.8 nm;the nanoemulsion had good stability.It is indicated that the preparation of compound rifaximin nanoemulsion is simple and the quality of the product is controllable.Our results provide a theoretical basis for the wide use of compound rifaximin in the treatment of intestinal bacterial infections in livestock and poultry.