Abstract: OBJECTIVE To prepare paclitaxel-Coix seed oil microemulsion using oil phase replacing microemulsion with Coix seed oil, to screening the optimal formula for the preparation of paclitaxel-Coix seed oil microemulsion and to conduct methodological studies on the determination of paclitaxel content. METHODS Different emulsifiers and auxiliary emulsifiers were selected, and water titration method was used to draw the pseudo ternary phase diagram, and the best emulsifier and auxiliary emulsifier were selected. By observing the milk formation, and the encapsulation efficiency and loading efficiency were selected as the indexes, the optimal formula to obtain paclitaxel-Coix oil microemulsion, and the zeta potential and particle size distribution were determined. RESULTS The formulation of paclitaxel-Coix seed oil microemulsion was paclitaxel(10 mg), HS 15 600 mg and polyethylene glycol 400 200 mg, Coix seed oil 200 mg and respectively. The encapsulation efficiency and drug loading efficiency of paclitaxel-Coix seed oil microemulsion were (98.9±1.26)% and (0.56±0.05)%, respectively. The paclitaxel-Coix seed oil microemulsion particle size was (35.23±1.20)nm and zeta potential was (-2.93±0.69)mV. CONCLUSION Paclitaxel-Coix seed oil microemulsion is successfully prepared in this study, which has a complete and uniform appearance, small particle size, high encapsulation efficiency, and certain drug sustained-release function.