Objective@#To evaluate the effect of levonorgestrel-releasing intrauterine system (LNG-IUS) plus oral megestrol acetate (MA) as fertility-preserving treatment in patients with early-stage endometrial cancer (EEC). @*Methods@#In this single-center, phase II study with open-label, randomized and controlled design, young patients (18–45 years) diagnosed with primary EEC were screened, who strongly required fertility-preserving treatment. Patients were randomly assigned (1:1) into MA group (160 mg oral daily) or MA (160 mg oral daily) plus LNG-IUS group. Pathologic evaluation on endometrium retrieved by hysteroscopy was performed every 3 months. The primary endpoint was complete response (CR) rate within 16 weeks of treatment. The secondary endpoints were CR rate within 32 weeks of treatment, adverse events, recurrent and pregnancy rate. @*Results@#Between July 2017 and June 2020, 63 patients were enrolled and randomly assigned. Totally 56 patients (26 in MA group; 28 in MA + LNG-IUS group) were included into primary-endpoint analyses. The median follow-up was 31.6 months (range, 3.1–94.0). No significant difference in 16-week CR rate were found between MA and MA + LNG-IUS groups (19.2% vs. 25.0%, p=0.610; odds ratio=1.40; 95% confidence interval=0.38–5.12), while the 32-week CR rates were also similar (57.1% and 61.5%, p=0.743), accordingly. More women in MA + LNG-IUS group experienced vaginal hemorrhage (46.4% vs. 16.1%; p=0.012) compared with MA group. No intergroup difference was found regarding recurrence or pregnancy rate. @*Conclusion@#Compared with MA alone, the addition of LNG-IUS may not improve the early CR rate for EEC, and may produce more adverse events instead.