Abstract： Objective:To evaluate the clinical efficacy and safety of oral mifepristone (10 mg/day) versus placebo in the preoperative treatment of uterine fibroids.Methods:This study was a multi-center, randomized, double-blind, placebo, parallel controlled trial. A total of 132 patients with uterine fibroids were randomly divided into study group and control group, with 66 cases in each group. The patients in the study group orally took 1 tablet/day of mifepristone (dose of 10 mg/tablet), the patients in the control group orally took 1 tablet/day of placebo, and both groups were treated for 3 months. The primary efficacy evaluation indicators were the change rate of maximum fibroid volume; the secondary efficacy evaluation indicators included amenorrhea rate, improvement of subjective symptoms and anemia; the safety evaluation indicators included the analysis of adverse events and changes in laboratory biochemical indicators.Results:At the end of treatment, the maximum leiomyoma volume was reduced by 25.97% (95% CI: -34.79%--15.95%) in the study group and reduced by 1.51% (95% CI: -13.03%-11.54%) in the control group. The change rate of the maximum leiomyoma volume before and after treatment in the study group was significantly greater than that in the control group, and the difference in the change rate of the maximum leiomyoma volume between the two groups was -24.84% (95% CI: -36.56%--10.94%), which was much higher than the 10% superiority threshold goal set by this study within the 95% CI interval. At the end of treatment, the complete amenorrhea rate [84% (52/62)], dysmenorrhea elimination rate [98% (61/62)], and menstrual blood loss disappearance rate [87% (54/62)] in the study group were significantly higher than those in the control group (all P<0.05). At the end of treatment, the mean hemoglobin [(131±13) g/L], red blood cell count [(4.5±0.4)×10 12/L] and hematocrit (0.39±0.03) in the study group were significantly increased compared with the baseline, and the differences had statistical significance (all P<0.05); after treatment, the differences in the above three indicators between the two groups had statistical significance (all P<0.01). The serum estradiol level in the study group was significantly lower than that in the control group at the end of treatment, and the difference was statistically significant ( P<0.01). There were no significant differences in follicle-stimulating hormone and cortisol levels before and after treatment between the two groups ( P>0.05). The overall incidences of any adverse event were not significantly different between the two groups (all P>0.05). Abdominal pain was the most common adverse event in the study group [9% (6/65)], but the incidence was not significantly increased compared with the control group [3% (2/64); P>0.05]. Conclusion:Compared with placebo, oral mifepristone 10 mg/day is significantly superior to placebo in reducing the size of uterine fibroids and improving anemia, without significant adverse reactions, and could be used as a drug treatment for patients with of uterine fibroids before surgery.